1. By Kelley Mortakis

2. A+B
• If A and B are two numbers, the sum
represents the total number of objects we will
have if we start with A objects and then get B
more objects.
• The numbers A and B in a sum are called
terms, addends, or summands.

3. A-B
• If A and B are two numbers, the difference
represents the total number of objects we
will have if we start with A objects and take
away B of those objects.
• The numbers A and B in a difference can be
called terms. The number A is sometimes
called the minuend, the number B is
sometimes called the subtrahend.

4. examples
If we start with 149 toothpicks and we get 85 more
toothpicks….
149+85
If we start with 142 toothpicks and give away 83
toothpicks....
142-83

5. Associative Property of Addition
• Tells us that when we add any three numbers,
it doesn’t matter whether we add the first two
and then add the third, or whether we add
the first number to the sum of the second and
the third- either way we will always get the
same answer.
• (A + B) + C = A + (B + C)

6. Examples
(2 + 3) + 4 = 2 + (3 + 4)
(738 + 99) + 1= 738 + (99 + 1)

7. Mental Methods for Multi-Digit
Addition and Subtraction
• Some methods children learn for single-digit
addition and subtraction generalize to multi-
digit situations; providing children with
flexible, quick ways to solve addition and
subtraction problems mentally.
• Make-a-Round-Number Method
• Rounding and Compensating
• Subtractions Problems as Unknown Addend
Problems

8. Make-a-Round-Number Method
• This uses the associative property of addition to
shift one piece of an addend and join the piece
with the other addend.
• If you look for a nice round number that is close
to one of the addends this method will work.
• Example: 376 + 199, mentally break 376 into 375
+ 1 and join the 1 with 199 to make 200.
Therefore the sum is 375+200=575.

9. Rounding and Compensating
• Another way to solve 376+199 is to round and
compensate: if we add 200 to 376 instead of
adding 199+376. This makes 576, but since we
added 1 too many, we must take away 1 from
567.
• 376+199= 376+200-1
• =576-1
• 575

10. Subtraction Problems as Unknown
Addend Problems
• If you view the subtraction problem as an
unknown addend problem it can be helpful in
solving multi-digit subtraction problems mentally.
• Example: 684 – 295=? If you view this problem as
295 + ?= 684.
• Start with 295 and add until we reach 684.
• 295+5=300, 300+300=600, 600+84=684
• All together we added 5+300+84=389.
• Therefore, 684 – 295=389