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The HCF of 18 and 24 is 6. Use the rule HCF × LCM = product of the two numbers to work out their LCM.

Class 6Playing with NumbersPlaying with Numbers
  • A72
  • B42
  • C108
  • D432

Step-by-Step Solution

, so the LCM is 432 ÷ 6 = 72. Listing confirms it: 18, 36, 54, 72 and 24, 48, 72 first meet at 72. The traps: 432 is the product itself, not the LCM, and 42 comes from adding 18 + 24 instead of multiplying.
Answer: A) 72

Key idea: HCF and LCM — the two ends of common ground

**HCF** (Highest Common Factor) is the biggest number that divides both numbers — it sits at the *small* end of common factors. **LCM** (Least Common Multiple) is the smallest number both numbers divide — it sits at the *small* end of common multiples (which is the *big* side of factors). For Class 6, the simplest method is listing: write all the factors (or first several multiples) of each number and pick the right one. Faster methods come in Class 7.

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