Question 20

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waecmaths question: 

What is the diameter of a circle of area 77cm2 (take $\pi =\tfrac{22}{7}$ ) 

Option A: 

$\tfrac{\sqrt{2}}{7}cm$

Option B: 

$3\tfrac{1}{2}cm$

Option C: 

7cm

Option D: 

$7\sqrt{2}cm$

waecmaths solution: 

$\begin{align}  & A=\frac{\pi {{d}^{2}}}{4} \\ & 77c{{m}^{2}}=\frac{22{{d}^{2}}}{7\times 4} \\ & {{d}^{2}}=\frac{77\times 7\times 4}{22}=49\times 2 \\ & d=\sqrt{49\times 2}=7\sqrt{2}cm \\\end{align}$

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