Question

A stoplight changes color every 15 seconds and Stoplight B changes color every 45 seconds. Both stoplights changed color 12 seconds ago. After how many seconds will the stoplights change color at the same time again?

Answer 1

After 33 seconds

Explanation:

Here in this question, we are interested in knowing the next time both spotlights will change color at the same time again.

From the question , we can identify that while one changes color at 15 seconds, the other changes at 45 seconds. Now, since 15 is a factor of 45(or let’s say 45 is a multiple of 15), the next time they would change color at the same time will be the 45 seconds from last time.

What this means is that they will be changing colors at the same time every 45 seconds. But in the case of this question, they both changed 12 seconds ago, so the next time they will be changing will be 45-12 = 33 seconds