A person observed that he required 30 seconds less time to cross a circular ground along its diameter than to cover it once along the boundary. If his speed was 30 m/minute, then the radius of the circular ground is $$(Take \pi=\frac{22}{7})$$
Let the radius of circular ground be $$r$$ and his speed is 30 m/min
=> Time required to cross along diameter = $$\frac{2r}{30}$$
Time required to cross along boundary = $$\frac{2 \pi r}{30}$$
Acc. to ques :
=> $$\frac{2 \pi r}{30} - \frac{2r}{30} = \frac{30}{60}$$
=> $$\pi r - r = \frac{15}{2}$$
=> $$r = \frac{15 * 7}{2 * 15}$$ = 3.5 m
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