The perimeter of a rhombus is 40 cm and one of its diagonals measures 12 cm. Find its area in ${\text{cm}}^2$.

Side = 40/4 = 10 cm. Half of the given diagonal is 6 cm, so the other half-diagonal = √$(10^2-6^2)=$ √64 = 8 cm and the second diagonal is 16 cm. Area = ½ × $12\times 16=96{\text{cm}}^2$.