Question

Assignment - 5.1
1. At two crossroads signals, lights change after every 25 seconds and 45
seconds respectively. If they changed together at 9:20 a.m., then when will
they change together next?
(A) at 9:23:45 a.m. (B) at 9:23:15 a.m.
(C) at 9:23:30 a.m. (D) at 9:23:00 a.m.​

Answer 1

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

this is your right anwer

Step-by-step explanation:

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