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HCF & LCM · Question 1 of 63

Question 1

EasyOriginal question

What is the least common multiple of 12, 18 and 24?

Options for question 1

Show the answer and explanation
CorrectNot quiteAnswer B

Correct answer: B

Explanation

  1. Write each number as a product of prime factors: 12=22×312 = 2^2 \times 3, 18=2×3218 = 2 \times 3^2 and 24=23×324 = 2^3 \times 3.

  2. The LCM takes the highest power of each prime that appears anywhere: 232^3 from 24 and 323^2 from 18.

  3. So the LCM is 23×32=8×9=722^3 \times 3^2 = 8 \times 9 = 72.

  4. Check: 72÷12=672 \div 12 = 6, 72÷18=472 \div 18 = 4 and 72÷24=372 \div 24 = 3, all whole numbers.

Worth noting

144 and 216 are common multiples too, but the question asks for the least one. Multiplying the numbers together always gives a common multiple and almost never the smallest.

Concept
LCM by prime factorisation
Typical time
45 s
Your time
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The rule this testsFinding HCF and LCM
Practise this chapter →

Ten questions from HCF & LCM, at your own pace.

Practise this chapter →

Ten questions from HCF & LCM, at your own pace.