If the area of a rectangle of length 24 cm is 40 sq. cm less than the area of a square of side 20 cm, then what is the perimeter of the rectangle?

Area of the square of side 20 cm = Side × Side = 20 cm × 20 cm = 400 sq. cm

It is given that area of the rectangle is 40 sq. cm less than the area of the square.

∴Area of the rectangle = (400 − 40) sq. cm = 360 sq. cm

Length of the rectangle = 24 cm

∴The breadth of the rectangle = $\frac{\mathrm{Area}}{\mathrm{Length}}=\frac{360}{24}=15 \mathrm{cm}$ 

∴Perimeter of the rectangle = 2 (Length + Breadth)

= 2 × (24 cm + 15 cm)

= 2 × 39 cm

= 78 cm