By what least number should 9900 be multiplied so that the product becomes a perfect square?
A5
B9
C11
D22
Answer & Solution
Correct answer: C. 11
Prime factorise $9900=2^2\times3^2\times5^2\times11$. For a perfect square, every prime must occur an even number of times. Only 11 has an odd exponent, so multiplying by 11 makes all exponents even. Then the product becomes a perfect square.
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