Subtraction can be carried out in two ways: by taking away (begin with 8 and take away 5) or by counting up (begin with 5 and count up to 8). Counting up is more like addition and may be easier for some students. We will use this "counting up" method as part of a strategy for mental subtraction.
Step by step | Subtraction by counting up
- Count up from the smaller number to the next ten. Remember this count.
- Count up from this ten to the larger number.
- Add this count to the first count to find the total difference.
Example | Subtraction by counting up
Q: 34 − 18
A: The difference of 34 and 18 can be found by counting up from 18 to 34. Beginning at 18, we first count up to 20, a count of 2. Next, we count up from 20 to 34, a count of 14. Lastly, we combine our counts: 2 + 14 = 16.