Question

There is a string of red and blue lights strung around a window . The red lights blink every 3 seconds , and the blue lights blink every 5 seconds , how many times will they blink at the same time in one minutes ?

Answer 1

They will blink 4 times per minute.

Explanation:

Count the time of the red lights: 3, 6, 9, 12, 15.

Count the time of the blue lights: 5, 10, 15.

Do you see the two 15s?