A red light blinks every 12 seconds and a blue light blinks every 9 seconds. When will both lights blink at the same time?

Answer 1

This problem requires that you determine the least common multiple of 9 and 12.

If you count by 9s and count by 12s, the first and least common multiple will be 36.

The lights will blink at the same time after 36 seconds.

NOTE: You could also use prime factorization to find the solution.