Question 4

At a telephone exchange, three phones ring at intervals of 20 sec, 24 sec and 30 seconds. If they ring together at 11:25 a.m, when will they next ring together?


We will take the LCM of 20, 24, 30, which is 120.

It tells us that they will together after an interval of 120 seconds = 2 minutes.

So, at 11:27 a.m they will next ring together.

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