waecmaths question:
The total surface area of a solid cylinder is 165cm2. If the base diameter is 7cm, calculate its height [Take $\pi =\tfrac{22}{7}$]
Option A:
7.5cm
Option B:
4.5cm
Option C:
4.0cm
Option D:
2.0cm
waecmaths solution:
$\begin{align} & A=165c{{m}^{2}} \\ & r=\frac{d}{2}=\frac{7}{2}cm \\ & A=2\pi r(r+h) \\ & 165=2\times \tfrac{22}{7}\times \tfrac{7}{2}(\tfrac{7}{2}+h) \\ & 165=22(\tfrac{7}{2}+h) \\ & 165=77+22h \\ & 22h=88 \\ & h=4cm \\\end{align}$
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