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