0580/23 May/Jun 2026, Question 6: HCF and LCM
Cambridge IGCSE Mathematics 0580 · Paper 23 (Extended) · Non-calculator · 3 marks
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The question, in short
Red flashes every 20 minutes and blue every 35 minutes; both flash together at 10 00. Find the next time they flash together.
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Solution · 3 marks
- 120 = 2 × 2 × 5, 35 = 5 × 7
- 2LCM = 2 × 2 × 5 × 7 = 140 minutes
- 3140 minutes = 2 hours 20 minutes
- 410 00 + 2 h 20 min = 12 20
Answer12 20
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