Question

Stoplight A 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

Answer: The stoplights will change color after 33 seconds . at the same time again.

Explanation:

Given: Stoplight A changes color every 15 seconds and Stoplight B changes color every 45 seconds.

Then, the number of seconds after which they change color at the same time again = least common multiple of 15 and 45.

Since, 15 = 5 x 3 , 45 = 3 x 3 x 5

Least common multiple of 15 and 45. = 3 x 3 x 5 = 45

Since, Both stoplights changed color 12 seconds ago.

So after 45-12 = 33 seconds .

Hence, the stoplights will change color after 33 seconds . at the same time again.