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A person observed that he required 30 s time to cross a circular ground along its diameter than to cover it once along the boundary. If his speed was 30m/min, then the radius of the circular ground is \( \Large (take \ \pi = 22/7) \)

A) 10.5 m
B) 3.5 m
C) 5.5 m
D) 7.5 m

Correct Answer:


B) 3.5 m

Description for Correct answer:

Let the radius of circular field = r m.

Speed of person in m/s =\( \Large \frac{30}{60}=\frac{1}{2} \)m/s

According to the question,

\( \Large \frac{2\pi r}{1/2}-\frac{2r}{1/2} \)=30 => \( \Large 4\pi r \)-4r=30

=> \( \Large \left(4\times 22/7 - 4 \right)r \)=30

=> (12.5-4)r=30 => (8.5)r=30

=> r=\( \Large \frac{30}{8.5} \)=3.5 m.

Part of solved Area and perimeter questions and answers : >> Elementary Mathematics >> Area and perimeter

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