Question

Top surface of a raised platform is in the shape of a regular octagon as shown in the figure. Find the area of the octagonal surface.

• A. $119m^2$
• B. $19m^2$
• C. $11.9m^2$
• D. None of these

Answer 1

The correct option is A $119m^2$

$\Rightarrow$Area of Trapezium$=\frac{1}{2}\left(Sumofparallellines\right)\times height$

$\Rightarrow$Area of the octagonal surface $ABCDEFGH$

$=Area(trap.ABCH)+Area(rect.HCDG)+Area(trap.GDEF)$

$=\left[\begin{array}{c}\frac{1}{2}(5+11)\times 4+(11\times 5)+\frac{1}{2}(11+5)\times 4\end{array}\right]m^2$

$=(32+55+32)m^2=119m^2$.