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

The alarm clocks will beep together again at the Least Common Multiple (LCM) of 20 and 25 minutes.

$\text{LCM of 20 and 25} = 100 \, \text{minutes}$

Thus, the next time they beep together will be 100 minutes after 12:00 PM, which is 1 hour and 40 minutes later, or 12:40 PM.