A Biker Travels 60 Miles In 2

A biker travels 60 miles in 2.5 hours. Determine the biker's average speed.

Solution
The equation relating distance, velocity and time provides

60 = V(5/2)

Divide both sides by 5/2 to solve for V.

V = (60)2/5 = 24 miles/hour

Example 16

A car travels between two cities 400 miles apart in 7 hours. The return trip takes 9 hours. Find the
average speed of the car.

Solution
The total distance is 2(400) = 800 miles. The total time is 7 + 9 = 16 hours. The average speed is found
from D = VT:

800 = V(16)

V = 800/16 = 50 miles/hour

Example 17

A police officer, traveling at 100 miles per hour, pursues Philip who has a 30 minute head start. The police
officer overtakes Philip in two hours. Find Philip's speed.

Solution
Let x miles per hour be Philip's speed. The distance traveled by the officer equals the distance traveled by
Philip:

2 × 100 = (2 + 30/60)x

200 = (2 + 0.5)x

200 = 2.5x therefore x = 80 mph

• A 555-mile, 5-hour plane trip was flown at two speeds. For the first part of the trip, the
average speed was 105 mph. Then the tailwind picked up, and the remainder of the trip
was flown at an average speed of 115 mph. For how long did the plane fly at each speed?

First I'll set up a grid: Copyright © Elizabeth Stapel 1999-2009 All Rights Reserved

d r t
first part d 105 t
second part 555 – d 115 5–t
total 555 --- 5

Using "d = rt", the first row gives me d = 105t and the second row gives me:

555 – d = 115(5 – t)

Since the two distances add up to 555, I'll add the two distance expressions, and set their sum
equal to the given total:

555 = 105t + 115(5 – t)

Then I'll solve:

555 = 105t + 575 – 115t
555 = 575 – 10t
–20 = –10t
2=t

According to my grid, "t" stands for the time spent on the first part of the trip, so my answer is
"The plane flew for two hours at 105 mph and three hours at 115 mph."

You can add distances and you can add times, but you cannot add rates. Think about it: If you drive 20
mph on one street, and 40 mph on another street, does that mean you averaged 60 mph?

As you can see, the actual math involved is often quite simple. It's the set-up that's the hard part. So what
follows are some more examples, but with just the set-up displayed.

• An executive drove from home at an average speed of 30 mph to an airport where a
helicopter was waiting. The executive boarded the helicopter and flew to the corporate
offices at an average speed of 60 mph. The entire distance was 150 miles; the entire trip
took three hours. Find the distance from the airport to the corporate offices.

d r t
driving d 30 t
flying 150 – d 60 3–t

total 150 --- 3

The first row gives me the equation d = 30t. Since the first part of his trip accounted for d miles of
the total 150-mile distance and t hours of the total 3-hour time, I am left with 150 – d miles and 3
– t hours for the second part. The second row gives me the equation:

150 – d = 60(3 – t)

Adding the two "distance" expressions and setting their sum equal to the given total distance, I
get:

150 = 30t + 60(3 – t)

Solve for t; interpret the value; state the final answer.

• A car and a bus set out at 2 p.m. from the same point, headed in the same direction. The
average speed of the car is 30 mph slower than twice the speed of the bus. In two hours,
the car is 20 miles ahead of the bus. Find the rate of the car.

d r t
car d + 20 2r – 30 2
bus d r 2
total --- --- ---

(As it turns out, I won't need the "total" row this time.) The first row gives me:

d + 20 = 2(2r – 30)

This is not terribly helpful. The second row gives me:

d = 2r

Use the second equation to simplify the first equation by substituting "2r" in for "d", and then
solve for "r". Interpret this value within the context of the exercise, and state the final answer.

• A passenger train leaves the train depot 2 hours after a freight train left the same depot.
The freight train is traveling 20 mph slower than the passenger train. Find the rate of each
train, if the passenger train overtakes the freight train in three hours.

d r t
passenger train d r 3
freight train d r – 20 3+2=5
total --- --- ---

(As it turns out, I won't need the "total" row this time.) Why is the distance just "d" for both trains?
Partly, that's because the problem doesn't say how far the trains actually went. But mostly it's
because they went the same distance as far as I'm concerned, because I'm only counting from
the depot to wherever they met. After that meet, I don't care what happens. And how did I get
those times? I know that the passenger train drove for three hours to catch up to the freight train;
that's how I got the "3". But note that the freight train had a two-hour head start. That means that
the freight train was going for five hours.

d r t
passenger train d = 3r r 3
freight train d = 5(r – 20) r – 20 3+2=5
total --- --- ---

Now that I have this information, I can try to find my equation. Using the fact that d = rt, the first
row gives me d = 3r (note the revised table above). The second row gives me:

d = 5(r – 20)

Since the distances are equal, I will set the equations equal:

3r = 5(r – 20)

Solve for r; interpret the value within the context of the exercise, and state the final answer.

• Two cyclists start at the same time from opposite ends of a course that is 45 miles long.
One cyclist is riding at 14 mph and the second cyclist is riding at 16 mph. How long after
they begin will they meet?

d r t
slow guy d 14 t
fast guy 45 – d 16 t
total 45 --- ---

Why is t the same for both cyclists? Because I am measuring from the time they both started to
the time they meet somewhere in the middle. And how did I get "d" and "45 – d" for the
distances? Because once I'd assigned the slow guy as having covered d miles, that left 45 – d
miles for the fast guy to cover: the two guys together covered the whole 45 miles.

Using "d = rt", I get d = 14t from the first row, and 45 – d = 16t from the second row. Since
these distances add up to 45, I will add the distance expressions and set equal to the given total:

45 = 14t + 16t

Solve for t.

• A boat travels for three hours with a current of 3 mph and then returns the same distance
against the current in four hours. What is the boat's speed in calm water? How far did the
boat travel one way?

d r t
downstream d b+3 3
upstream d b–3 4
total 2d --- 7

(It may turn out that I won't need the "total" row.)

I have used "b" to indicate the boat's speed. Why are the rates "b + 3" and "b – 3"? Because I
actually have two speeds combined into one on each trip. The boat has a certain speed (the
"speed in calm water" that I'm looking for; this is the speed that registers on the speedometer),
and the water has a certain speed (this is the "current"). When the boat is going with the current,
the water's speed is added to the boat's speed. This makes sense, if you think about it: even if
you cut the engine, the boat would still be moving, because the water would be carrying it
downstream. When the boat is going against the current, the water's speed is subtracted from the
boat's speed. This makes sense, too: if the water is going fast enough, the boat will still be going
downstream (a "negative" speed, because the boat would be going backwards at this point),
because the water is more powerful than the boat. (Think of a boat in a cartoon heading toward a
waterfall. The guy paddles like crazy, but he still goes over the edge.)

d r t
downstream d = 3(b + 3) b+3 3
upstream d = 4(b – 3) b–3 4
total 2d --- 7

Using "d = rt", the first row (of the revised table above) gives me:

d = 3(b + 3)

The second row gives me:

d = 4(b – 3)

Since these distances are the same, I will set them equal:

3(b + 3) = 4(b – 3)

Solve for b. Then back-solve for d.

In this case, I didn't need the "total" row.

• With the wind, an airplane travels 1120 miles in seven hours. Against the wind, it takes
eight hours. Find the rate of the plane in still air and the velocity of the wind.

d r t
tailwind 1120 p+w 7
headwind 1120 p–w 8
total 2240 --- 15

(I probably won't need the "total" row.) Just as with the last problem, I am really dealing with two
rates together: the plane's speedometer reading, and the wind speed. When the plane turns
around, the wind is no longer pushing the plane to go faster, but is instead pushing against the
plane to slow it down. Copyright © Elizabeth Stapel 1999-2009 All Rights Reserved

The first row gives me:

1120 = 7(p + w)

The second row gives me:

1120 = 8(p – w)

The temptation is to just set these equal, like I did with the last problem, but that just gives me:

7(p + w) = 8(p – w)

...which doesn't help much. I need to get rid of one of the variables.

I'll take that first equation:

1120 = 7(p + w)

...and divide through by 7:

160 = p + w

Then, subtracting w from either side, I get that p = 160 – w. I'll substitute "160 – w" for "p" in the
second equation:

1120 = 8([160 – w] – w)

1120 = 8(160 – 2w)

...and solve for w. Then I'll back-solve to find p.

• A spike is hammered into a train rail. You are standing at the other end of the rail. You
hear the sound of the hammer strike both through the air and through the rail itself. These
sounds arrive at your point six seconds apart. You know that sound travels through air at
1100 feet per second and through steel at 16,500 feet per second. How far away is that
spike?

d r t
air d = 1100t 1100 t
steel d = 16,500(t – 6) 16,500 t–6
total --- --- 6

However long the sound took to travel through the air, it took six seconds less to propagate
through the steel. (Since the speed through the steel is faster, then that travel-time must be
shorter.) I multiply the rate by the time to get the values for the distance column. (Once again, I
didn't need the "total" row.)

Since the distances are the same, I set the distance expressions equal to get:

1100t = 16,500(t – 6)

Solve for the time t, and then back-solve for the distance d by plugging t into either expression for
the distance d.

Adding To The Solution

Mixture Problems: Example 1:

John has 20 ounces of a 20% of salt solution, How much salt should he add to make it a 25%
solution?

Solution:

Step 1: Set up a table for salt.

original added result
concentration
amount

Step 2: Fill in the table with information given in the question.

John has 20 ounces of a 20% of salt solution. How much salt should he add to make it a 25%
solution?

The salt added is 100% salt, which is 1 in decimal.
Change all the percent to decimals

Let x = amount of salt added. The result would be 20 + x.

concentration 0.2 1 0.25
amount 20 x 20 + x

Step 3: Multiply down each column.

amount 20 x 20 + x
multiply 0.2 × 20 1×x 0.25(20 + x)

Step 4: original + added = result

0.2 × 20 + 1 × x = 0.25(20 + x)
4 + x = 5 + 0.25x

Isolate variable x
x – 0.25x = 5 – 4
0.75x = 1

Answer: He should add ounces of salt.

Removing From The Solution


John has 20 ounces of a 20% of salt solution. How much water should he evaporate to make it a
30% solution?

Solution:

Step 1: Set up a table for water. The water is removed from the original.

original removed result
concentration

amount


John has 20 ounces of a 20% of salt solution. How much water should he evaporate to make it a
30% solution?

The original concentration of water is 100% – 20% = 80%
The resulted concentration of water is 100% – 30% = 70%
The water evaporated is 100% water, which is 1 in decimal.

Change all the percent to decimals.

Let x = amount of water evaporated. The result would be 20 – x.

amount 20 x 20 – x


amount 20 x 20 – x
multiply 0.8 × 20 1×x 0.70(20 – x)

Step 4: Since the water is removed, we need to subtract

original – removed = result
0.8 × 20 – 1 × x = 0.70(20 – x)
16 – x = 14 – 0.7x

Isolate variable x
x – 0.7x = 16 – 14
0.3x = 2

Answer: He should evaporate 6.67 ounces of water.

Replacing The Solution


A tank has a capacity of 10 gallons. When it is full, it contains 15% alcohol. How many gallons
must be replaced by an 80% alcohol solution to give 10 gallons of 70% solution?

Solution:

Step 1: Set up a table for alcohol. The alcohol is replaced i.e. removed and added.

original removed added result
concentration
amount


A tank has a capacity of 10 gallons. When it is full, it contains 15% alcohol. How many gallons
must be replaced by an 80% alcohol solution to give 10 gallons of 70% solution?

Change all the percent to decimals.

Let x = amount of alcohol solution replaced.

concentration 0.15 0.15 0.8 0.7
amount 10 x x 10


concentration 0.15 0.15 0.8 0.7
amount 10 x x 10
multiply 0.15 × 10 0.15 × x 0.8 × x 0.7 × 10

Step 4: Since the alcohol solution is replaced, we need to subtract and add.

original – removed + added = result
0.15 × 10 – 0.15 × x + 0.8 × x = 0.7 × 10
1.5 – 0.15x + 0.8x = 7

Isolate variable x
0.8x – 0.15x = 7 – 1.5

0.65x = 5.5

Answer: 8.46 gallons of alcohol solution needs to be replaced.

Mixing Quantities Of Different Costs


How many pounds of chocolate worth $1.20 a pound must be mixed with 10 pounds of chocolate
worth 90 cents a pound to produce a mixture worth $1.00 a pound?

Solution:

Step 1: Set up a table for different types of chocolate.

cost
amount


How many pounds of chocolate worth $1.20 a pound must be mixed with 10 pounds of chocolate
worth 90 cents a pound to produce a mixture worth $1.00 a pound?

Let x = amount of chocolate added.

cost 0.9 1.2 1
amount 10 x x + 10


cost 0.9 1.2 1
amount 10 x x + 10
multiply 0.9 × 10 1.2 × x 1 × (x + 10)

Step 4: original + added = result

0.9 × 10 + 1.2 × x = 1 × (x + 10)
9 + 1.2x = x + 10

Isolate variable x
1.2x – x = 10 - 9
0.2x = 1

Answer: 5 pounds of the $1.20 chocolate needs to be added.

Word Problems: Mixtures
In order to solve problems involving mixture, it is necessary to

 solve one variable equations involving: one step, two steps, multi-steps
 analyze and understand the problem
 write and solve an equation for the problem

Even though there are two different types of mixes, the process for solving them is the same.

 dry mixture created from two differently priced components such as two types of
candy or two types of nuts
 liquid mixture of a specific strength made from two or more solutions having
differing concentrations

Suppose the owner of a candy store mixes two types of candies. She decides to create a 20-
pound mixture of raspberry-flavored gumdrops and cherry-flavored jelly beans. The
gumdrops sell for $0.95 per pound and the jelly beans sell for $1.20 per pound. She plans to
sell the mix for $1.10 per pound. How many pounds of each candy should she use in her
mix?

First, since two quantities are to be mixed together to produce one mixture, we need to
recognize that we will set up an equation that shows the following:

total cost of gumdrops plus total cost of jelly beans equals the total cost of mixture

To arrive at the equation, it is typically helpful to use a table illustrating the problem such as
the following:

Type of Candy
Cost of Candy
(unit price)
Amount of
Candy
(in pounds)
Total Cost
(in dollars)

gumdrops

jelly beans

mixture

The first column shows the types of candy involved, cost is displayed in the second column,
amount of each type of candy is listed in the third column, and the fourth column is the
product of each cost and each amount for each type of candy. The total cost of the mixture is
found by multiplying the cost of each type candy times the amount of each type of candy
used in the mixture. The total cost column will be used to write the equation.

The candy store owner knows that she wants the total amount of the mixture of candy to be
20 pounds. However, she does not know how many pounds of each type to mix. That is the
objective of the problem. So in the “Amount of Candy” column we will use x to represent
the amount of gumdrops. Then the “total pounds of candy minus x” will represent the
amount of jelly beans: (20 – x). The last column demonstrates that the price of each type
candy multiplied times the amount of each type candy represents the total cost of each type
candy. The last column is what we use to write the equation.

Remember:

total cost of gumdrops plus total cost of jelly beans equals the total cost of mixture

So, using the information in the last column:

We are ready to solve the equation to find the amount of each type of candy the store owner
should use in her mixture.

First distribute to remove
parentheses

Now multiply the equation by 100

Solve for x

pounds

Since x represents the amount of gumdrops to be used in the mixture the candy store owner
will use 8 pounds of gumdrops. From column three of the table, you can see that the amount
of jelly beans to be used is (20 - x). Substituting 8 for the x, we see that the store owner
needs to use (20 - 8) which is 12 pounds of jelly beans to create the desired mix.

We have now learned the candy store owner will mix 8 pounds of raspberry-flavored
gumdrops that cost $0.95 per pound and 12 pounds of cherry-flavored jelly beans that cost
$1.20 per pound to create a mixture of 20 pounds of candy that sells for $1.10 per pound.

Let's Practice

Qu
esti
on
#1

A
loc
al
gro
cer
has
dec
ide
d to
mix
100
pou
nds
of
cas
he
ws
and
alm
ond
s
for
a
holi
day

This type of problem requires carefully setting up a table using the information given in the
problem. Following the development of the table, a linear equation must be written and solved.
Using the information written in the last column of the table, set up your equation in this format:

total amount of item one plus total amount of item two equals total amount of the mixture

After writing the equation and solving for the unknown variable, always check to be certain that
the answer obtained answers the question and/or question(s) asked in the problem. It is always
advisable to substitute your answers back into the equation to check that your solution is correct.

Kuta Software - Infinite Algebra 1 Name___________________________________
Period___Mixture Word Problems Date________________ _
1) 2 m³ of soil containing 35% sand was mixed
into 6 m³ of soil containing 15% sand. What
is the sand content of the mixture?
2) 9 lbs. of mixed nuts containing 55% peanuts
were mixed with 6 lbs. of another kind of
mixed nuts that contain 40% peanuts. What
percent of the new mixture is peanuts?
3) 5 fl. oz. of a 2% alcohol solution was mixed
with 11 fl. oz. of a 66% alcohol solution.
Find the concentration of the new mixture.
4) 16 lb of Brand M Cinnamon was made by
combining 12 lb of Indonesian cinnamon
which costs $19/lb with 4 lb of Thai
cinnamon which costs $11/lb. Find the cost
per lb of the mixture.
5) Emily mixed together 9 gal. of Brand A fruit
drink and 8 gal. of Brand B fruit drink
which contains 48% fruit juice. Find the
percent of fruit juice in Brand A if the
mixture contained 30% fruit juice.
6) How many mg of a metal containing 45%
nickel must be combined with 6 mg of pure
nickel to form an alloy containing 78%
nickel?
7) How much soil containing 45% sand do you need
to add to 1 ft³ of soil containing 15% sand in order
to make a soil containing 35% sand?
8) 9 gal. of a sugar solution was mixed with 6
gal. of a 90% sugar solution to make a 84%
sugar solution. Find the percent
concentration of the first solution.
9) A metallurgist needs to make 12.4 lb. of an

alloy containing 50% gold. He is going to
melt and combine one metal that is 60%
gold with another metal that is 40% gold.
How much of each should he use?
10) Brand X sells 21 oz. bags of mixed nuts that
contain 29% peanuts. To make their
product they combine Brand A mixed nuts
which contain 35% peanuts and Brand B
mixed nuts which contain 25% peanuts.
How much of each do they need to use?
Period___Mixture Word Problems Date________________ _
1) 2 m³ of soil containing 35% sand was mixed
into 6 m³ of soil containing 15% sand. What
is the sand content of the mixture?
20%
2) 9 lbs. of mixed nuts containing 55% peanuts
were mixed with 6 lbs. of another kind of
mixed nuts that contain 40% peanuts. What
percent of the new mixture is peanuts?
49%
3) 5 fl. oz. of a 2% alcohol solution was mixed
with 11 fl. oz. of a 66% alcohol solution.
Find the concentration of the new mixture.
46%
4) 16 lb of Brand M Cinnamon was made by
combining 12 lb of Indonesian cinnamon
which costs $19/lb with 4 lb of Thai
cinnamon which costs $11/lb. Find the cost
per lb of the mixture.
$17/lb
5) Emily mixed together 9 gal. of Brand A fruit
drink and 8 gal. of Brand B fruit drink
which contains 48% fruit juice. Find the
percent of fruit juice in Brand A if the
mixture contained 30% fruit juice.
14%
6) How many mg of a metal containing 45%
nickel must be combined with 6 mg of pure
nickel to form an alloy containing 78%
nickel?
4 mg
7) How much soil containing 45% sand do you need
to add to 1 ft³ of soil containing 15% sand in order
to make a soil containing 35% sand?
2 ft³

8) 9 gal. of a sugar solution was mixed with 6
gal. of a 90% sugar solution to make a 84%
sugar solution. Find the percent
concentration of the first solution.
80%
9) A metallurgist needs to make 12.4 lb. of an
alloy containing 50% gold. He is going to
melt and combine one metal that is 60%
gold with another metal that is 40% gold.
How much of each should he use?
6.2 lb. of 60% gold, 6.2 lb. of 40% gold
10) Brand X sells 21 oz. bags of mixed nuts that
contain 29% peanuts. To make their
product they combine Brand A mixed nuts
which contain 35% peanuts and Brand B
mixed nuts which contain 25% peanuts.
How much of each do they need to use?
8.4 oz. of Brand A, 12.6 oz. of Brand B

8 John has $20,000 to invest. He invests part of his money at an annual interest rate of 6%, the
rest at 9% annual rate. The return on these two investments over one year is $1,440. How much
does he invest at each rate?

Solution
Paul made two investments totaling $15,000. The percentage return on the first investment
was 7% annually, while the the percentage return on the second one was 10% annually. If the
total return on the two investments over one year was $1,350, how much was invested at each
rate?

Ben invested $30,000, part of which at 5% annual interest rate, the rest at 9% annual interest
rate. The interest earned from the investments was $2,100 at the end of one year. How much did
he invest at each rate?

Solution
Jason invested $20,000 for one year, Part of his money was invested at an annual interest rate
of 6%, the rest at an annual interest rate of 10%. If his total income from the two investments
over one year was $1,700, how much was invested at each rate?

5% annual interest. the rest into another account paying 8% annual interest. If the total interest
earned at the end of one year was $1,390, how much was invested at each account?

annual interest rate. The total interest earned over the 6 month period was $450, how much was
invested at each rate?

Solution

and the rest at 10% annual interest rate. If the total income for three months from the investments
was $240, how much was invested at each rate?

Sue has $15,000 to invest for 5 months, part at 6% annual rate, the rest at 10% annual rate. If
the total interest earned at the end of five months is $450, how much was invested at each rate?

1. Lisa requires additional income to meet her everyday expenses. She has $30,000 to
invest. To generate the required additional income, the annual return rate has to be 6%.
She deposits part of her capital into an account paying 4% per year, and invest the rest in
stocks earning 10% per year. How much does she need to invest at each rate?

2. To balance risk and return on his investment, Ben invests part of his money in an low
risk, low return bank saving account paying 5% per year, the rest in high risk, high return
stocks earning 15% per year. To achieve the goal of a 12% annual return on $24,000
investment, how much does he need to invest at each rate?

3. Sue has invested $12,000 at an annual interest rate of 6%. To realize an annual return of
8% on her investment, how much more funds must she invest at an annual rate of 12%?

4. Paul deposited $21,000 into his bank saving account paying 5% per year. How much
additional funds must he invest at 10% annually so that the annual return on his total
investment is 7%?

5. Joe made two investments. She earned 8% annually on her first investment, but lost 12%
annually on her second investment. If her total investment was $15,000, and the total
income was $240 for one year, how much money was allocated to each investment?

6. Allan made two investments totaling $20,000. He earned 5% annually on his first
investment, but lost 10% annually on his second investment. If the net loss was $140 for

one year, how much money was allocated to each investment?

7. Jan made two investments. She made a 7% profit on her first investment, but lost 10%
annually on her second investment. If her total investment was $16,000, and the total
income was $100, how much money was allocated to each investment?

8. Paul made two investments totaling $25,000. He made a profit of 6% on his first
investment, but made a loss of 10% on his second investment. If the net loss was $260,
how much money was allocated to each investment?

9. Ben invests 30% of his total funds at 5% annual rate, the rest at 8% annual rate. If his
total income for one year is $625, how much does he invest at each rate?

10. Ben invests 30% of his total funds at 5% annual rate, 40% at 6% annual rate, the rest at
8% annual rate. If his total income for one year is $560, how much does he invest at each
rate?
11. 1 A certain amount of money is to be invested for a period of one year. The amount of
money invested at 6% per year is twice as much as the amount invested at 9% per year. If
the income for one year is $1680, how much is invested at each rate?

Solution

12. 1 Jeff has some money to invest for one year. The amount of money invested at 5% per
year is $5,000 more than that invested at 8% per year. The interest earned is $1,160. How
much does he invest at each rate?

Solution

13. 1 One third of the funds is invested at an annual interest rate of 4%, the rest at 6%
annual rate. If the income for one year is $480, how much is invested at each rate?

14. 1 The ratio of the the amount of money invested at 6% annual rate to the amount
invested at 9% is 2 : 5. If the total income for one year is $570, how much is invested at
each rate?

15. 1 A certain amount of money is to be invested for one year. The amount of money
invested at 6% per year is $2,000 more than twice the amount invested at 9% per year. If
the income for one year is $1,800, how much is invested at each rate?

16. 1 John has some money to invest, the amount of money invested at 5% per year is
$3,000 less than three times the amount invested at 9% per year. If the income for one
year is $1,050, how much is invested at each rate?

Worker A can produce 20 auto parts per hour, while worker B can produce 30 auto parts per
hour. How long will it take for both of them, working together, to produce 1,000 auto parts?
Detailed solution to this problem

2. Relative rate of work

Example:

Working alone, worker A can complete a task in 3 hours, worker B can complete it in 6 hours.
How long will it take for both of them, working together, to complete the task?
Detailed solution to this problem

More similar problems

3. Man-hours

Example

If 20 workers can complete a task in 12 hours, how long would it take for 30 workers?

"Work" Problems: Two Persons

Example 1:

Peter can mow the lawn in 40 minutes and John can mow the lawn in 60 minutes. How long will
it take for them to mow the lawn together?

Solution:

Step 1: Assign variables:

Let x = time to mow lawn together

Step 2: Use the formula:

Step 3: Solve the equation

The LCM of 40 and 60 is 120
Multiply both sides with 120

Answer: The time taken for both of them to mow the lawn together is 24 minutes.

“Work” Problems: More than Two Persons

Example 1:

Jane, Paul and Peter can finish painting the fence in 2 hours. If Jane does the job alone she can
finish it in 5 hours. If Paul does the job alone he can finish it in 6 hours. How long will it take for
Peter to finish the job alone?

Solution:


Let x = time taken by Peter



Multiply both sides with 30x

Answer: The time taken for Peter to paint the fence alone is hours.

“Work” Problems: Pipes Filling up a Tank

Example 1:

A tank can be filled by pipe A in 3 hours and by pipe B in 5 hours. When the tank is full, it can
be drained by pipe C in 4 hours. if the tank is initially empty and all three pipes are open, how
many hours will it take to fill up the tank?

Solution:


Let x = time taken to fill up the tank


Since pipe C drains the water it is subtracted.


The LCM of 3, 4 and 5 is 60

Multiply both sides with 60

Answer: The time taken to fill the tank is hours.

Period___Work Word Problems Date________________ _
Solve each question. Round your answer to the nearest hundredth.
1) Working alone, Ryan can dig a 10 ft by 10 ft
hole in five hours. Castel can dig the same
hole in six hours. How long would it take
them if they worked together?
2) Shawna can pour a large concrete driveway
in six hours. Dan can pour the same
driveway in seven hours. Find how long it
would take them if they worked together.
3) It takes Trevon ten hours to clean an attic.

Cody can clean the same attic in seven
hours. Find how long it would take them if
they worked together.
4) Working alone, Carlos can oil the lanes in a
bowling alley in five hours. Jenny can oil
the same lanes in nine hours. If they worked
together how long would it take them?
5) Working together, Paul and Daniel can pick
forty bushels of apples in 4.95 hours. Had
he done it alone it would have taken Daniel
9 hours. Find how long it would take Paul
to do it alone.
6) Working together, Jenny and Natalie can
mop a warehouse in 5.14 hours. Had she
done it alone it would have taken Natalie 12
hours. How long would it take Jenny to do
it alone?
7) Rob can tar a roof in nine hours. One day
his friend Kayla helped him and it only took
4.74 hours. How long would it take Kayla
to do it alone?
8) Working alone, it takes Kristin 11 hours to
harvest a field. Kayla can harvest the same
field in 16 hours. Find how long it would
take them if they worked together.
9) Krystal can wax a floor in 16 minutes. One
day her friend Perry helped her and it only
took 5.76 minutes. How long would it take
Perry to do it alone?
10) Working alone, Dan can sweep a porch in
15 minutes. Alberto can sweep the same
porch in 11 minutes. If they worked
11) Ryan can paint a fence in ten hours. Asanji
can paint the same fence in eight hours. If
they worked together how long would it take
them?
12) Working alone, it takes Asanji eight hours to
dig a 10 ft by 10 ft hole. Brenda can dig the
same hole in nine hours. How long would it
take them if they worked together?
Period___Work Word Problems Date________________ _
Solve each question. Round your answer to the nearest hundredth.
1) Working alone, Ryan can dig a 10 ft by 10 ft
hole in five hours. Castel can dig the same

hole in six hours. How long would it take
them if they worked together?
2.73 hours
2) Shawna can pour a large concrete driveway
in six hours. Dan can pour the same
driveway in seven hours. Find how long it
would take them if they worked together.
3.23 hours
3) It takes Trevon ten hours to clean an attic.
Cody can clean the same attic in seven
hours. Find how long it would take them if
they worked together.
4.12 hours
4) Working alone, Carlos can oil the lanes in a
bowling alley in five hours. Jenny can oil
the same lanes in nine hours. If they worked
3.21 hours
5) Working together, Paul and Daniel can pick
forty bushels of apples in 4.95 hours. Had
he done it alone it would have taken Daniel
9 hours. Find how long it would take Paul
to do it alone.
11 hours
6) Working together, Jenny and Natalie can
mop a warehouse in 5.14 hours. Had she
done it alone it would have taken Natalie 12
hours. How long would it take Jenny to do
it alone?
8.99 hours
7) Rob can tar a roof in nine hours. One day
his friend Kayla helped him and it only took
4.74 hours. How long would it take Kayla
to do it alone?
10.01 hours
8) Working alone, it takes Kristin 11 hours to
harvest a field. Kayla can harvest the same
field in 16 hours. Find how long it would
take them if they worked together.
6.52 hours
9) Krystal can wax a floor in 16 minutes. One
day her friend Perry helped her and it only
took 5.76 minutes. How long would it take
Perry to do it alone?
9 minutes
10) Working alone, Dan can sweep a porch in

15 minutes. Alberto can sweep the same
porch in 11 minutes. If they worked
6.35 minutes
11) Ryan can paint a fence in ten hours. Asanji
can paint the same fence in eight hours. If
they worked together how long would it take
them?
4.44 hours
12) Working alone, it takes Asanji eight hours to
dig a 10 ft by 10 ft hole. Brenda can dig the
same hole in nine hours. How long would it
take them if they worked together?
4.24 hours

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