three bells toll at intervals of 9 12 15 minutes. If they start tolling together, after what time will they toll next?

The options for above question is

a.1 hrs

b.2 hrs

c.3 hrs

d.4 hrs

Logically the next time when they ring together will be a factor(least possible minutes) common to all 3 bellls

so we need to take LCM of 9 ,12 and 15

image 3

Calculating from the above steps

LCM = 2 × 2 × 3 × 3 × 1 ×1 × 5 = 180

∴ Time after which the three bells will ring together next = 180 minutes

using formula 60 minutes = 1 hour

∴ 180 minutes = 180 / 60 = 3 hours

the ans is c. 3 hrs

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