The traffic lights at 3 different road crossings change after every 48 sec, 72 sec and 108 sec, respectively. If they all change simultaneously at 8:20 a.m., then at what time will they next change again simultaneously?
Answer & explanation
Correct answer: option 1
48 = 24 × 3
72 = 23 × 32
108 = 22 × 33
LCM ( 48, 72, 108) = 24 × 33 = 432
After 432 seconds, they will change simultaneously.
432 seconds ⇒ 7 minutes 12 seconds
Lights will change at 8:20:00 + 7 minutes + 12 seconds = 8:27:12 hours