Put the larger number on top and line up the columns. Subtract the ones first. If the top digit is smaller than the bottom digit, exchange one from the column to the left.
An exchange turns 1 ten into 10 ones, or 1 hundred into 10 tens. The value of the number does not change, only how it is written. Check every subtraction by adding the answer to the number you took away.
Worked example
Work out 704 − 268
- Ones: 4 − 8 does not work and there are no tens, so exchange a hundred for 10 tens, then a ten for 10 ones.
- 14 − 8 = 6, 9 − 6 = 3, 6 − 2 = 4.
Answer:436
Key words
- exchange
- swap one of a bigger unit for ten of the next
- subtract
- take away
- check
- add back to see if you get the top number
Practise this
New questions every time.
Common Core-referenced: 3.NBT.A.2