Most HCF and LCM puzzles are word problems. The skill is deciding which one you need: things that happen again and again and meet are about multiples (LCM); cutting or packing into the biggest equal groups is about factors (HCF).
Worked example: Two bells ring every 12 minutes and every 18 minutes. They ring together at 9:00. After how many minutes will they next ring together? 36 min
They meet again at a common multiple of 12 and 18 — the smallest one is the LCM.
Count in 18s: 18, 36. 36 ÷ 12 = 3 exactly, so the LCM is 36.
Check: 36 = 12 × 3 = 18 × 2, and no smaller number (like 18 or 24) is divisible by both ✓
Work it out on paper, then tap the answer you think is right. Stuck? Press “Show me how” to see every step.
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🏁 Topic 8 test
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