#numbers-4

By what least number should 8640 be multiplied to result in perfect square?

 a)12   b)14    c)15   (d)20


Solution:-

 8640 ends with a  Zero ...so option c or d must be the answer

 8640=16 *560 = (2^6 * 3^3 *5 )
For a perfect square the power of index of primes must be multiple of 2

 (2^6 * 3^3 *5 )(2^0 * 3^1 * 5^1)

  Answer:-15


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