Three bells are ringing at intervals of 20, 30 and 40 minutes respectively. At what time will they ring together again, if they ring simultaneously at 9 a.m?
- 11:30 am
- 10 am
- 11 am
- None of these
Explanation
Find LCM of 20, 30, and 40:
Prime factors:
20 = 2² × 5
30 = 2 × 3 × 5
40 = 2³ × 5
LCM = 2³ × 3 × 5 = 120 minutes
120 minutes = 2 hours, so if they ring together at 9:00 am, they will ring together again at 11:00 am.
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