Division and multiplication together

Division and multiplication together

Division and multiplication together

Earlier articles said that division is the opposite of multiplication. Now let's see what that really means — and how one multiplication fact gives you four problems.

Three numbers, four problems

Take three numbers that belong together — for example 3, 4, 12, because 3 × 4 = 12.

From these three numbers you can build four different problems:

3 × 4 = 12

4 × 3 = 12 (thanks to commutativity)

12 ÷ 3 = 4

12 ÷ 4 = 3

We call this trio of numbers a fact family. They're related like a family.

Three numbers and the four problems you can build from them

Why this is useful

Less practice, more knowledge. When you remember that 6 × 7 = 42, you immediately also know:
  • 7 × 6 = 42
  • 42 ÷ 6 = 7
  • 42 ÷ 7 = 6
Four facts from one.

Try it yourself

Family 2, 5, 10 (because 2 × 5 = 10):

  • 2 × 5 = 10
  • 5 × 2 = 10
  • 10 ÷ 2 = 5
  • 10 ÷ 5 = 2

Family 4, 6, 24 (because 4 × 6 = 24):

  • 4 × 6 = 24
  • 6 × 4 = 24
  • 24 ÷ 4 = 6
  • 24 ÷ 6 = 4

Family 3, 3, 9 (special — when the factors are the same):

  • 3 × 3 = 9
  • 9 ÷ 3 = 3

When the factors are the same, the family only has 2 problems — one multiplication and one division.

A trick for solving division

When you meet a division whose answer you don't remember, switch to multiplication.

Example: 35 ÷ 5 = ?

Ask yourself: "Five times what equals thirty-five?"

  • 5 × 5 = 25 (too small)
  • 5 × 6 = 30 (too small)
  • 5 × 7 = 35

So 35 ÷ 5 = 7.

Summary

  • Three numbers in a fact family make four equations — two multiplications and two divisions.
  • When you remember one multiplication fact, you automatically know four facts.
  • For division, ask "X times what = Y?" and switch to multiplication.
  • When the factors are the same, the family only has 2 problems.