Question

Two neon lights are turned on at the same time. One blinks every 4 seconds and the other blinks every 6 seconds. In 60 seconds, how many times will they blink at the same time?

Answer 1

You have to multiple 321 by 3, so the answer would be 963.

Answer 2

Find common multiples of 4 and 6:
4 8 12 16 20 24 28 32 36 40 44 48 52 56 60
6 12 18 24 30 36 42 48 54 60 At 12,24,36,48,60
They match. Another way of looking at it is find LCM of 4 and 6, which is 12 then just count by 12's 60/12 = 5

In 60 sec, they blink at the same time 5 times

Hope this is helpful!