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 need to list multiples of 4 and 6 until 60. Find which multiples are shared, i.e. 12 is a multiple of 4 and 6. Count how many multiples are multiples of both 4 and 6. 

Answer 2

4 will blink 15 times and 6 will blink 10. together they will blink 25 times