Question

An electronic device makes a beep every 15 minutes. Another device makes a beep after every 20 minutes. They beeped together at 6 a.m. At what time will they next beep together?

Answer 1

The LCM of the time intervals of the beeps will give the time when the electronic devices will beep together.
LCM of 15 and 20:

Required time = 5 × 3 × 2 × 2
= 60 min
So, they will beep simultaneously after 60 min or 1 h. 

∴ They will beep together again at 7:00 a.m.