Primes, HCF and LCM

Primes, HCF and LCM

Secondary 1

Three lights flash every \(15\) seconds, \(20\) seconds and \(24\) seconds respectively. They flash together at \(10:00\) a.m.

  1. When will they next flash together?

  2. How many times will all three flash together during the next \(10\) minutes? Exclude the initial flash at \(10:00\) a.m., but include the flash at \(10:10\) a.m.

Solution:

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Answer:(a) \( 10{:}02\text{ a.m.} \) (b) \( 5\text{ times} \).

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