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- 1. MATH: COMPUTATIONAL SKILLS Section I DePaul Math Placement Test
- 4. The most basic form of mathematical expressions involving several mathematical operations can only be solved by using the order of PEMDAS . This catchy acronym stands for: Parentheses : first, perform the operations in the innermost parentheses. A set of parentheses supercedes any other operation. Exponents : before you do any other operation, raise all the required bases to the prescribed exponent. Exponents include roots, since root operations are the equivalent of raising a base to the 1 / n, where ‘n’ is any integer. Multiplication and Division : perform multiplication and division. Addition and Subtraction : perform addition and subtraction. Order of Operations
- 5. Here are two examples illustrating the usage of PEMDAS . Let’s work through a few examples to see how order of operations and PEMDAS work. 3 X 2 3 + 6÷4. Since nothing is enclosed in parentheses, the first operation we carry out is exponentiation: 3 X 2 3 + 6÷4 = 38+6÷4 Next, we do all the necessary multiplication and division: 3 X 8+6÷4 = 24÷1.5 Lastly, we perform the required addition and subtraction. Our final answer is: 24÷1.5= 25.5 Here a few question to try yourself. Evaluate : 6 (2 3 2(5-3)) Hint: Start solving from the innermost parenthesis first (Final Answer is 12). Here’s another question. Evaluate: 5-2 2 ⁄6+4. Hint: Solve the numerator and denominator separately. Order of Operations: Examples
- 7. In order to add or subtract numbers with exponents, you must first find the value of each power, then add the two numbers . For example, to add 3 3 + 4 2 , you must expand the exponents to get (3x 3 x 3) + (4 x 4), and then, 27 + 16 = 43. However, algebraic expressions that have the same bases and exponents, such a s 3 x 4 and 5 x 4 , c an be added and subtracted. For exampl e, 3 x 4 + 5 x 4 = 8 x 4 . Adding and Subtracting Numbers with Exponents
- 8. To multiply exponential numbers raised to the same exponen t , raise their product to that exponent: a n x b n = (ax b) n = (ab) n 4 3 x 5 3 =(4x5) 3 = 20 3 To divide exponential numbers raised to the same exponen t , raise their quotient to that exponent: a n /b n = (a/b) n 12 5 / 3 5 = (12/3) 5 = 4 3 To multiply exponential numbers or terms that have the same base , add the exponents together: a m b n = (ab) (m+n) 3 6 x3 2 = 3 (6+2) = 3 8 To divide two same-base exponential numbers or terms , just subtract the exponents: a m /b n = (a/b) (m-n) 3 6 /3 2 = 3 (6-2) = 3 4 When an exponent is raised to another exponent in cases, (3 2 ) 4 and (x 4 ) 3 . In such cases, multiply the exponents: (a m ) n = a (mn) (3 2 ) 4 = 3 (2x 4) = 3 8 Multiplying and Dividing Numbers with Exponents
- 11. Fractional Exponents Exponents can be fractions, too. When a number or term is raised to a fractional power, it is called taking the root of that number or term. This expression can be converted into a more convenient form: x (a/b) = b For example, 2 13 ⁄ 5 is equal to the fifth root of 2 to the thirteenth power: 13 = 6.063 The symbol is also known as the radical, and anything under the radical (in this case 2 13 ) is called the radicand. For a more familiar example, look at 9 1⁄2 , which is the same as : 1 = = 2
- 12. Negative Exponents Seeing a negative number as a power may be a little strange the first time around. But the principle at work is simple. Any number or term raised to a negative power is equal to the reciprocal of that base raised to the opposite power. For example: x -5 = (1/ x 5 ) Or a slightly more complicated example: (2/3) -3 =(1/(2/3)) -3 = (3/2) 3 = 27/8 Now You’ve got the four rules of special exponents. Here are some examples to firm up your knowledge: x (1/8) = 1 = 4 2/3 x 4 8/5 = 4 (2/3 +8/5) = 4 (34/15) = 34 (3 -2 ) x = 3 -2 x = 1/3 2x 3(xy) 0 = 3 b -1 = 1/b x - 2/3 x z -2/3 = (xz) -2/3 = 1/( 2 ) 1 2x/3w4 = 1 ( one raised to any power is still one)
- 13. Roots and Radicals We just saw that roots express fractional exponents. But it is often easier to work with roots in a different format. When a number or term is raised to a fractional power, the expression can be converted into one involving a root in the following way: x 5/3 = 5 with the √sign as the radical sign and x a as the radicand . Roots are like exponents, only backward. For example, to square the number 3 is to multiple 3 by itself two times: 3 2 = 3 x 3 = 9. The root of 9, is 3. In other words, the square root of a number is the number that, when squared, is equal to the given number.
- 14. Square Roots and Cube Roots Square roots are the most commonly used roots, but there are also Cube roots (numbers raised to 1 / 3 ), fourth roots, fifth roots, and so on. Each root is represented by a radical sign with the appropriate number next to it (a radical without any superscript denotes a square root). cube roots are shown a s and fourth roots as . These roots of higher degrees operate the same way square roots do. Because 3 3 = 27, it follows that the cube root of 27 is 3. Here are a few examples: = 4 because 4 2 =16 = ½ because (1/2) 2 = ¼ I f x n = y, then = x The same rules that apply to multiplying and dividing exponential terms with the same exponent apply to roots as well. Consider these examples: X = = 4 X = Just be sure that the roots are of the same degree (i.e., you are multiplying or dividing all square roots or all roots of the fifth power).
- 17. Reducing fractions makes life with fractions much simpler. It makes unwieldy fractions, such as 450 / 600 , smaller and easier to work with . To reduce a fraction to lowest terms, divide the numerator and denominator by their greatest common factor. For example, for 450 / 600 , the GCF of 450 and 600 i s 150. The fraction reduces to 3 / 4 . A fraction is in reduced form if its numerator and denominator are relatively prime (their GCF is 1). Therefore, it makes sense that the equivalent fractions we studied in the previous section all reduce to the same fraction. For example , the equivalent fractions 4 / 6 and 8 / 12 both reduce to 2 / 3 . Reducing Fractions
- 18. When dealing with integers, large positive numbers with a lot of digits, like 5,000,000 , are greater than numbers with fewer digits, such as 5. 200 / 20,000 might seem like an impressive fraction, bu t 2 / 3 is actually larger because 2 is a much bigger part o f 3 than 200 is of 20,000. Cross-multiplication: While dealing with two fractions that have different numerators and denominators, such as 200 / 20,000 and 2 / 3 ., a n easy way to compare these two fractions is to use cross multiplication. Simply multiply the numerator of each fraction by the denominator of the other. then write the product of each multiplication next to the numerator you used to get it. We’ll cross-multiply 200 / 20,000 and 2 / 3 : 600 = 200 2 = 40,000 20,000 3 Since 40,000 > 600, 2 / 3 is the greater fraction. Comparing Fractions
- 19. On the math placement test you will need to know how to add and subtract two different types of fractions. The fractions will either have the same or different denominators. Fractions with the Same Denominators Fractions are extremely easy to add and subtract if they have the same denominator. In addition problems, all you have to do is add up the numerators: 1 + 3 + 13 = 17 20 20 20 20 Subtraction works similarly. If the denominators of the fractions are equal, then you simply subtract one numerator from the other: 13 – 2 = 11 20 20 20 Adding and Subtracting Fractions
- 22. A mixed number is an integer followed by a fraction, like 1 1 / 2 . It is another form of an improper fraction, which is a fraction greater than one. But any operation such as addition, subtraction, multiplication, or division can be performed only on the improper fraction form, so you need to know how to convert between the two. Let’s convert the mixed number 1 1 / 2 into an improper fraction. You multiply the integer portion of the mixed number by the denominator and add that product to the numerator. So 1 x 2 + 1 = 3, making 3 the numerator of the improper fraction. Pu t 3 over the original denominator , 2, and you have your converted fraction, 3 / 2 . Here’s another example: 3 2 / 13 = (3x13) +2 = 41 13 13 Mixed Numbers
- 23. The least common multiple (LCM) of two integers is the smallest multiple that the two numbers have in common. Like the GCF, the least common multiple of two numbers is useful when manipulating fractions. To find the LCM of two integers, you must first find the integers’ prime factorizations. The least common multiple is the smallest prime factorization that contains every prime number in each of the two original prime factorizations. If the same prime factor appears in the prime factorizations of both integers, multiply the factor by the greatest number of times it appears in the factorization of either number. For example, what is the least common multiple of 4 and 6? We must first find their prime factorizations. 4 = 2 x 2 Least Common Multiple
- 24. Let’s try a harder question. Q. What is the LCM of 14 and 38 ? A. we start by finding the prime factorizations of both numbers: 14= 2 x 7 38= 2 x 19 Here 2 appears in both prime factorizations, but not more than once in each, so we only need to use one 2. Therefore, the LCM of 7 and 38 is 2x 7 x 18 =266 For practice, find the LCM of the following pairs of integers: 12 and 32 15 and 26 34 and 40 Compare your answers to the solutions: 12 = 2 3 X3. 32 = 2 5 . The LCM is 2 5 X 3 = 96. 15 = 3 X 5. 26 = 2 X 13. The LCM is 2 X 3 X 5 X 13 = 390. 34 = 2 X 17. 40 = 2 3 X 5. The LCM is 2 3 X 5 X 17 = 680. Least Common Multiple
- 25. Decimals are just another way to express fractions. To produce a decimal, divide the numerator of a fraction by the denominator. For example, 1 / 2 = 1÷2 = .5. Comparing Decimals As with fractions, comparing decimals can be a bit deceptive. As a general rule, when comparing two decimals such as .3 with .003, the decimal with more leading zeros is smaller. But if asked to compare . 003 with .0009, however, you might overlook the additional zero and, because 9 is the larger integer, choose . 0009 as the larger decimal. That, of course, would be wrong. Take care to avoid such mistakes. One way is to line up the decimal points of the two decimals: .0009 is smaller than . 0030 Similarly, . 000900 is smaller than .000925 Decimals
- 26. Let’s convert .3875 into a fraction and see how this First, we eliminate the decimal point and make 3875 the numerator: .3875 = 3875 ? Since .3875 has four digits after the decimal point, we put four zeros in the denominator: .3875 = 3875 1000 Then, by finding the greatest common factor of 3875 and 10000, 125, we can reduce the fraction: 3875 = 31 1000 80 To convert from fractions back to decimals is a cinch. Simply carry out the necessary division on your calculator, such as for 31 / 80 : 3 = 3÷ 5= 0.6 5 Converting Decimal Fractions
- 27. Percents A percent is another way to describe a part of a whole (which means that percents are also another way to talk about fractions or decimals). Percent literally means “of 100” in Latin, so when you attend school 25 percent of the time, that means you only go to school 25 / 100 (or .25) of the time. Take a look at this example : 3 is what percent of 15? This question presents you with a whole, 15, and then asks you to determine how much of that whole 3 represents in percentage form. Since a percent is “of 100,” to solve the question, you have to set the fraction 3 / 15 equal to x / 100 : 3 = x 15 100 You then cross-multiply .07 X 1100 = 7% of 1100=77 .97 X 13 = 97% of 13 =12.61