The traffic lights at two different road crossings change after every 54 sec and 76 sec, respectively. If they change simultaneously at 10:15:00 hours, then find the time at which they will change again simultaneously.

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SSC GD Constable (2022) Official Paper (Held On : 09 Feb 2023 Shift 2)
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  1. 10:34:12 hours
  2. 10:59:12 hours
  3. 10:52:34 hours
  4. 10:49:12 hours

Answer (Detailed Solution Below)

Option 4 : 10:49:12 hours
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Detailed Solution

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Given

The time period of first light = 54 seconds

The time period of the second light = 76 seconds

Concept:

Two events with different periods will coincide again after a time equal to the least common multiple (LCM) of their periods.

Solution:

⇒ LCM of 54 and 76 = 2052 seconds = 34 minutes 12 second

⇒ Add this to the start time of 10:15:00 + 00:34:12

Therefore, the lights will change again simultaneously at 10:49:12.

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