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Three lightships flash simultaneously at 6.00am. The first lightship flashes after every 12 seconds, and the second lightship every 30 seconds, and the third lightship every 66 seconds. A t what time will the three light ships next flash together?

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6:09am

6:10am

6:11am

6:12am

answer is C.

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Detailed Solution

Three beacons simultaneously at 6am. The first beacon flashes every 12 seconds, the second beacon every 30 seconds, and the third beacon every 66 seconds.
Then we take a common multiple of 12, 30 or 66.
That is

So, three lightships next flash together = 660 seconds = 11 minutes
The time next flashes is after 11 minutes = 6.11 A.M
Hence, option 3 is correct.

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