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HCF & LCM · Question 63 of 63

Question 63

HardOriginal question

The students of a school can be arranged exactly in rows of 6, of 8 or of 10. The number of students is also a perfect square. What is the least possible number of students?

Options for question 63

Show the answer and explanation
CorrectNot quiteAnswer D

Correct answer: D

Explanation

  1. The number is a multiple of LCM⁡(6,8,10)=120=23×3×5\operatorname{LCM}(6, 8, 10) = 120 = 2^3 \times 3 \times 5.

  2. For a perfect square every prime needs an even power: raise to 24×32×522^4 \times 3^2 \times 5^2.

  3. That is 120×30=3,600=602120 \times 30 = 3{,}600 = 60^2.

Worth noting

480=120×4480 = 120 \times 4 multiplies by a square, which never fixes the odd powers; 1,200 still has an odd power of 3.

Concept
Smallest perfect-square multiple of an LCM
Typical time
110 s
Your time
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The rule this testsHCF and LCM word problems
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Ten questions from HCF & LCM, at your own pace.

Practise this chapter →

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