On a road, three consecutive traffic lights change after $36, 42$ and $72$ seconds. If the lights are first switched on at $9 : 00 A M$ , then at what time will they change simultaneously?

9 : 08 : 04

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9 : 08 : 24

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9 : 08 : 44

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9 : 08 : 58

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Solution

The correct option is D $9 : 08 : 24$
The lights will change simultaneously after every interval = (LCM of $36, 42$ and $72$ ) seconds
LCM $= 2 \times 2 \times 3 \times 3 \times \times 2 \times 7 = 504$
$504$ seconds $= 8$ minutes and $24$ seconds
The next change will be at $9 : 08 : 24$ .

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On a road, three consecutive traffic lights change after 36,42 and 72 seconds. If the lights are first switched on at 9:00AM, then at what time will they change simultaneously?

The correct option is D 9:08:24The lights will change simultaneously after every interval = (LCM of 36,42 and 72) secondsLCM =2×2×3×3××2×7=504504 seconds =8 minutes and 24 secondsThe next change will be at 9:08:24.

On a road, three consecutive traffic lights change after $36, 42$ and $72$ seconds. If the lights are first switched on at $9 : 00 A M$ , then at what time will they change simultaneously?

The correct option is D $9 : 08 : 24$
The lights will change simultaneously after every interval = (LCM of $36, 42$ and $72$ ) seconds
LCM $= 2 \times 2 \times 3 \times 3 \times \times 2 \times 7 = 504$
$504$ seconds $= 8$ minutes and $24$ seconds
The next change will be at $9 : 08 : 24$ .