Mental Math: Subtraction Strategies

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Show your work for each problem.

1.
Which strategy is best for calculating ?
1. a)Standard algorithm
2. b)Breaking apart by place value
3. c)Counting up (since 58 and 63 are close together)
4. d)Compensation (round 58 to 60)
2.
Calculate using the counting up strategy. What is the answer?
3.
Use compensation to calculate . What is the answer?
4.
Calculate using the breaking apart strategy.
5.
When using compensation for , you first calculate . What do you do next?
1. a)Add 2 to get 37
2. b)The answer is already 35
3. c)Add 30 to get 65
4. d)Subtract 2 to get 33
6.
Calculate using the complement strategy (9 minus tens, 10 minus ones).
7.
Calculate using the counting up strategy.
8.
A book costs 38 euros. You pay with a 50 euro note. Using mental math, how much change should you receive?
1. a)18 euros
2. b)12 euros
3. c)22 euros
4. d)8 euros
9.
Calculate mentally.
10.
Calculate 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 ?
1. a), then
2. b), then
3. c), then
4. d), then
14.
Calculate using any mental math strategy.
15.
You have 75 euros. After buying a gift for 48 euros, how much money do you have left?