Find the least number by which 45 must be multiplied to obtain a perfect square.

Explanation

Prime-factorise:

45=3^2×5.

For a perfect square, every prime must have an even exponent. The exponent of 3 is already 2, but the exponent of 5 is only 1. Multiply by another 5:

45×5=225=15^2.

Therefore the least multiplier is 5.