How to subtract 9, 18 or 19 in your head

For ages 9 to 11 (Years 5 and 6) · 2-minute read · free worksheet

Taking away numbers like 9, 18 or 19 is awkward. Taking away a round number is easy, so we swap and then adjust.

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Worksheet includes an answer key for grown-ups

How it works

  1. Swap the number for a round one (18 becomes 20).
  2. Take the round number away.
  3. Give back the extra you took.

Worked example

49 − 18: 49 − 20 = 29. We took 2 too many, so give 2 back: 31.

Top tip

Same idea with single digits: 60 − 8 = 60 − 10 + 2 = 52.
How to subtract 9, 18 or 19 in your head: 49 − 18 = ? 49 − 20 = 29, give 2 back = 31

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