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WAEC Mathematics 2011 Paper

Question : 10

Total: 47

Solution:

A prism has 3 rectangular faces and 2 triangular faces and 2 rectangular faces = 10(3 + 4 + 5) = 120

Area of triangular faces =

\sqrt{s(s - a)(s - b)(s - c)}

where s =

\; \frac{a\;+\;b\;+\;c}{2}

\; \frac{3\;+\;4\;+\;5}{2}

\; \frac{12}{2}

= 6

Area of

\triangle

\sqrt{6(6 - 30(6 - 4)(6 - 5)}

\sqrt{6 \times 3 \times 2 \times 1}

= 6

Area of triangle faces = 2 x 6 = 12cm²

Total surface area = Area of rectangular face + Area of

\triangle

= 120 + 12

= 132cm²

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