Question

Ginny wants to build a square shaped wall using some square shaped bricks. How many bricks can she use to build the wall?

• A. 169
• B. 91
• C. 120
• D. None of these

Answer 1

The correct option is A 169

To make a square shaped wall using square bricks, length of all 4 sides of the wall must be equal.

This is possible only if Ginni uses equal number of square-shaped bricks on each side of the wall.
Hence, total number of bricks must be a perfect square.

Prime factorisation of 169 = $13\times 13$
$\Rightarrow$ 169 is a perfect square.

Prime factorisation of 91 = $7\times 13$
$\Rightarrow$ 91 is not a perfect square.

Prime factorisation of 120 = $2\times 2\times 2\times 3\times 5$
$\Rightarrow$ 120 is not a perfect square.

Out of the given options, only 169 is a perfect square.
$\therefore$ Ginny can use 169 square shaped bricks to build the square shaped wall.