Mental Math: Subtraction Strategies

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Show your work for each problem.

1.
The numbers in $63 - 58$ are close together. Which strategy from this lesson fits best?
1. a)Standard written algorithm
2. b)Counting up (since 58 and 63 are close together)
3. c)Compensation (round 58 to 60)
4. d)Breaking apart by place value
2.
Calculate $50 - 23$ using the counting up strategy. What is the answer?
3.
Use compensation to calculate $74 - 29$ . What is the answer?
4.
Calculate $86 - 43$ using the breaking apart strategy.
5.
When using compensation for $65 - 28$ , you first calculate $65 - 30 = 35$ . What do you do next?
1. a)Subtract 2 to get 33
2. b)The answer is already 35
3. c)Add 30 to get 65
4. d)Add 2 to get 37
6.
Calculate $100 - 47$ using the complement strategy (9 minus tens, 10 minus ones).
7.
Calculate $92 - 47$ using the counting up strategy.
8.
A book costs 38 dollars. You pay with a 50 dollar bill. Using mental math, how much change should you receive?
1. a)22 dollars
2. b)18 dollars
3. c)8 dollars
4. d)12 dollars
9.
Calculate $100 - 72$ mentally.
10.
Calculate $83 - 49$ using the compensation strategy.
11.
Your team scored 91 points. The opponent scored 67 points. What is the point difference?
12.
A movie is 95 minutes long. You've watched 58 minutes. How many minutes are left?
13.
Which calculation shows the correct use of compensation for $72 - 38$ ?
1. a) $70 - 40 = 30$ , then $30 + 2 = 32$
2. b) $72 - 40 = 32$ , then $32 - 2 = 30$
3. c) $72 - 40 = 32$ , then $32 + 2 = 34$
4. d) $72 - 38 = 32$ , then $32 + 2 = 34$
14.
Calculate $100 - 84$ using any mental math strategy.
15.
You have 75 dollars. After buying a gift for 48 dollars, how much money do you have left?