Take From Ten to Subtract

Every teen number holds a ten. 14 is 10 and 4.

Take from the ten

For 14 − 8, the 4 is too small to take 8 from. So take the 8 from the ten instead.

10 − 8 = 2. Then put back the 4 that was waiting. 2 + 4 = 6.

Why it works

You never lost anything. You only chose which part to take from.

The idea behind taking from ten

Every teen number is a ten plus some ones: 14 is 10 and 4, 16 is 10 and 6. When you subtract a number bigger than the ones, the ones alone are not enough. So take the whole amount out of the ten instead, then add the ones back on.

A worked case: 14 - 6

Step 1: split 14 into 10 and 4. Step 2: take 6 from the 10, leaving 4. Step 3: add back the 4 that was set aside: 4 + 4 = 8. So 14 - 6 = 8. Notice the last step is a double — the strategies keep helping each other.

When to reach for it

Use this when the number you are subtracting is bigger than the ones digit, like 15 - 8 or 13 - 9. When the ones digit is big enough — 17 - 4, say — do not bother; just take 4 from the 7. Part of getting good at maths is knowing when a strategy is not needed.