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Mathematics · Grades 4–7

Least common multiple

Use positive whole numbers. A common multiple is divisible by both.

Make a worksheet

The key idea

Use positive whole numbers. A common multiple is divisible by both.

lcm(a,b) = |ab| / gcd(a,b)

Worked examples

Find the least common multiple of 9 and 19.

9 × 19 ÷ 1 = 171

171

Find the least common multiple of 15 and 23.

15 × 23 ÷ 1 = 345

345

Try it yourself

  1. Find the least common multiple of 10 and 30.

  2. Find the least common multiple of 20 and 21.

Check your understanding

Answers and marking notes
  1. 30

    10 × 30 ÷ 10 = 30

  2. 420

    20 × 21 ÷ 1 = 420

Further reading and review references

These are reference links, not copied exercises, institutional endorsement or proof of independent review.

Learning preview · teacher review required. Grade bands are approximate, not official curriculum alignment.