Question

Six bells commence tolling together and each of them tolls at an interval of 2, 4, 6, 8, 10 and 12 seconds respectively. In 30 minutes, how many times do they toll together?

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Answer 1

L.C.M. of 2, 4, 6, 8, 10 and 12 is 120.
So, the bells will toll together after every 120 seconds (2 minutes).
In 30 minutes, they will toll together $\frac{30}{2}$ + 1 = 16 times.