Question

The traffic lights at three different road crossing change after every 48 seconds , 72 seconds and 108 seconds respectively. If they change simultaneously at 7 am , at what time will they change simultaneously again?

Answer 1

Find LCM:

48 = 2⁴ x 3

72 = 2³ x 3²

108 = 2² x 3³

LCM = 2⁴ x 3³ = 423

.

Convert 432 sec to min and sec:

432 = 432 ÷ 60 = 7 mins 12 sec

.

Next time it will change simultaneously = 7 am + 7 mins 12 sec = 7:07:12 am

.

Answer: 7:07:12 am

Answer 2

Answer:

Find LCM:

48 = 2⁴ x 3

72 = 2³ x 3²

108 = 2² x 3³

LCM = 2⁴ x 3³ = 423

.

Convert 432 sec to min and sec:

432 = 432 ÷ 60 = 7 mins 12 sec

.

Next time it will change simultaneously = 7 am + 7 mins 12 sec = 7:07:12 am

.

Answer: 7:07:12 am

Step-by-step explanation: