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4 alarm clocks ring together at 5 am. They ring after 7, 8, 11 and 12 seconds respectively. How many times will they ring together again in the next 3 hours?

4 alarm clocks ring together at 5 am. They ring after 7, 8, 11 and 12 seconds respectively. How many times will they ring together again in the next 3 hours? Correct Answer 5

Calculation:

All 4 bells ring together = LCM of (7, 8, 11, 12) = 1848 secs

3 hours = 3600 ×  3 = 10800 secs

Number of times = 10800/1848 = 5.84 ≈ 5 times 

∴ The number of times 4 bell ring together in next 3 hours is 5

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