Question

The traffice lights are three different road crossings change after every 48 seconds, 72 seconds, and
108 seconds respectively. If they change simultaneously at 7 a.m., at what time will they change
simultaneously again?

Answer 1

Answer:

7:07:12 a.m

Step-by-step explanation:

LCM of 48,72&108 will be the no. of seconds after which they will change simultaneously again.

LCM is 432.

i.e after 432 seconds they will change

simultaneously again.

So, Time =7 hrs+ 432sec=7hrs +7 min +2 sec =7:07:12 a.m

Answer 2

Answer:

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 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

Step-by-step explanation: