Question

Two alarm clocks ring their alarms at regular intervals of 20 minutes and 25 minutes respectively. If they first beep together at 12 noon, at what time will they beep again together next time?

Answer 1

Given that,

Two alarms ring at regular intervals of 20 and 25 minutes, respectively.

The time they will beep together again is their LCM.

So, LCM (20, 25)

20 = 2 × 2 × 5

25 = 5 × 5

LCM (20, 25) = 2 × 2 × 5 × 5 = 100

So, they will beep together after 100 minutes or 1 hour 40 minutes.

They will beep again after 12 noon at 1:40 pm.