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Mental math strategies

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The question

55 × 7 + 45 × 7

55 × 7 + 45 × 7=(55 + 45) × 7
(55 + 45) × 7=100 × 7
100 × 7=700
  1. Both products share a factor, so add the other two numbers first.
  2. Work out the easy part first: (55 + 45) × 7 = 100 × 7.
  3. Then finish: 100 × 7 = 700.

How it works.

  1. 01

    Both products share a factor, so add the other two numbers first.

  2. 02

    Work out the easy part first: (55 + 45) × 7 = 100 × 7.

  3. 03

    Then finish: 100 × 7 = 700.