Column addition and subtraction
Lesson 6 of 12
Column subtraction with exchange
Objective. Subtract two-digit numbers, exchanging a ten when needed.
The key idea
If the top ones digit is too small, exchange one ten for ten ones before subtracting.
Worked example
Calculate 62 − 27.
- 12 − 7 is not possible, so exchange a ten: 62 becomes 50 and 12.
- 212 − 7 = 5.
- 350 − 20 = 30.
Answer: 35
Practice
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