A circular swimming pool is surrounded by a wall with a height of 2m. The area of the wall is 21%

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[GMAT math practice question]

A circular swimming pool is surrounded by a wall with a height of 2m. The area of the wall is 21% of the area of the swimming pool. What is the area of the swimming pool?

A. 400π m^2
B. 300πm^2
C. 250πm^2
D. 200πm^2
E. 100πm^2
Source: — Problem Solving |

Junior | Next Rank: 30 Posts
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This seems like a poor quality/incomplete question.

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Assume the radius of the swimming pool is r.
Then the area of the wall is 2πr·2 = 4πr.
Since we have 4πr = (21/100) πr^2, we have 21r^2 – 400r + 400 = 0 or (21r + 20)(r - 20) = 0.
Thus, we have r = 20.
Then, the area of the swimming pool is πr^2 = 400π.

Therefore, A is the answer.
Answer: A