Question

The traffic lights at three different road crossings change after every 48 seconds, 72 seconds and 108 seconds. If they change simultaneously at 9 a.m.,after what time will they change again simultaneously.​

Answer 1

Answer:

Explanation: We know that in order to find the time when the three lights will change simultaneously again after 7 a.m., we need to find the LCM of 48, 72, and 108. Hence, converting 432 seconds into minutes and seconds, we get: 432 seconds = 7 minutes and 1

Answer 2

Answer:

7:07:12 a.m or 432 seconds = 7 min 12 seconds

Step-by-step explanation:

The traffic light at three different road crossing change after every 48 seconds,72 seconds and 108 seconds, respectively.

So let us take the LCM of the given time that is 48 seconds, 72 seconds, 108 seconds

⇒ 48 = 2 × 2 × 2 × 2 × 3

⇒ 72 = 2 × 2 × 2 × 3 × 3

⇒ 108 = 2 × 2 × 3 × 3 × 3

Hence, LCM of 48, 72 and 108 = (2 × 2 × 2 × 2 × 3 × 3 × 3)

LCM of 48, 72 and 108 = 432

So  after 432 seconds, they will change simultaneously

We know that

60 seconds = 1 minute

so on dividing 432 / 60, we get 7 as quotient and 12 as a reminder

Hence, 432 seconds = 7 min 12 seconds

∴ The time  = 7 a.m. + 7 minutes 12 seconds

Hence, the lights change simultaneously at  7:07:12 a.m