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?

8:27:12 a.m.

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