WAEC Mathematics 2011 Paper

Concept:Total surface area of a prism = (lateral surface area) + (area of the two triangular bases).Explanation:The triangular cross-section has sides $3\text{ cm}$, $4\text{ cm}$, and $5\text{ cm}$. Since $3^2 + 4^2 = 9 + 16 = 25 = 5^2$, it is a right-angled triangle.Area of one triangular base = $\frac{1}{2} \times 3 \times 4 = 6\text{ cm}^2$.Area of two triangular bases = $2 \times 6 = 12\text{ cm}^2$.The prism has its length as $10\text{ cm}$.Perimeter of the triangular base = $3 + 4 + 5 = 12\text{ cm}$.Lateral (rectangular) surface area = perimeter $\times$ length = $12 \times 10 = 120\text{ cm}^2$.Total surface area = $120 + 12 = 132\text{ cm}^2$.Answer:$132\text{ cm}^2$ (Option B).