Question

Which is the smallest number that has to be multiplied to make 1620 a perfect square?

• A. 3
• B. 5
• C. 7
• D. 2

Answer 1

The correct option is B 5

$$\begin{array}{cc}2& 1620\\ 2& 810\\ 3& 405\\ 3& 135\\ 3& 45\\ 3& 15\\ & 5\end{array}$$
So, $1620=2^2\times 3^2\times 3^2\times 5$
Since all the factors are not in pairs, 1620 is not a perfect square .
If we multiply 1620 with 5, then we get a perfect square.
Hence, 5 is smallest number to be multiplied to get perfect square.