Question

Signal A beeps every 15 seconds

signal B beeps every 40 seconds
signal C beeps every 100 seconds
the three signals start beeping at the same time
how many times in 1 hour will they start beeping at the same time again

Answer 1

15 = 3 × 5

40 = 2 × 2 × 2 × 5

100 = 2 × 2 × 5 × 5

LCM of 15, 40, and 100:

2 × 2 × 2 × 3 × 5 × 5 = 600

The three signals will beep at the same time every 600 seconds (10 minutes). So in one hour (60 minutes), the three signals will beep at the same time 6 times.