waecmaths question:
The surface area of a sphere is $\tfrac{792}{7}c{{m}^{2}}$. Find, correct to the nearest whole number, its volume [Take $\pi =\tfrac{22}{7}$]
Option A:
113cm3
Option B:
131cm3
Option C:
311cm3
Option D:
414cm3
waecmaths solution:
$\begin{align} & \text{Surface area of sphere}=A=4\pi {{r}^{2}} \\ & 4\pi {{r}^{2}}=\frac{792}{7}c{{m}^{2}} \\ & {{r}^{2}}=\frac{792c{{m}^{2}}}{7\times 4\pi }=\frac{792\times 7}{7\times 4\times 22}=9c{{m}^{2}} \\ & r=3cm \\ & \text{Volume of a sphere}=\frac{4}{3}\pi {{r}^{3}} \\ & V=\frac{4}{3}\times \frac{22}{7}\times {{3}^{3}}\approx 113c{{m}^{3}} \\\end{align}$
maths year:
maths topics: