1 More or 1 Less
Introduction, Stage 5 – Mental Multiplication
When combined with the other earlier skills, the strategy of using ‘1 more’ or ‘1 less’ is effective for calculating the remaining multiplication facts.
For example, 9 × 7 is one 7 less than 10 × 7. So 9 × 7 = 70 – 7 = 63. This works for all 9’s.
Similarly, 3 × 7 is one more 7 than doubling 7, so 3 × 7 = 7 + 14 = 21. This works for all 3’s.