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). Since counting by tens comes easily to many students, we will count up by tens as part of a strategy for mental subtraction.
Step by step | Subtraction by counting tens
- Count up from the smaller number by tens.
- Stop counting as close to the larger number as possible, without going over. Remember this count.
- Count on to the larger number. Add this count to the first count to find the total difference.
Example | Subtraction by counting tens
Q: 48 − 26
A: The difference of 48 and 26 can be found by counting up from 26 to 48. Beginning
at 26, we first count by tens up to 46, a count of 20. Counting on to 48 yields 2 more, which
we add to the count to find the total difference:
20 + 2 = 22.