Question

Find the number whose square is the sum of the cube of the first 5 natural numbers.

• A. 10
• B. 12
• C. 13
• D. 15

Answer 1

The correct option is D

15

The sum of first 5 natural numbers can be expressed as ${\left(\frac{n(n+1)}{2}\right)}^2$ where n = 5, which gives us
${\left(\frac{(5\times 6)}{2}\right)}^2$ =${\left(\frac{30}{2}\right)}^2$ = ${15}^2$
Thus the cubes of first 5 natural numbers can be expressed as the square of 15.