The traffic lights at three different road crossings change after 24 seconds, 36 seconds, and 54 seconds respectively. If they all change simultaneously at 10:15:00 AM, then at what time will they again change simultaneously ?

Answer: Option B

LCM of left(24, 36, 54)
⇒ 12 × 2 × 3 × 3 = 216 sec
⇒ They will change simultaneously after every 216 seconds
⇒ $$\frac{216}{60}$$ ⇒ $$3\frac{36}{60}$$ ⇒ 3 minute 36 seconds
⇒ They change 1^st at 10:15:00 AM
So, again they change at = 10:18:36 AM