A) 25 min
B) 20 min
C) 50 min
D) 100 min
Correct Answer: C
Solution :
Circumference \[=2\pi r=\frac{44}{7}\times r\,\,\text{m}\] |
Distance covered in 8 times \[=16\pi r\,\,\text{m}\] |
\[\therefore \] \[\text{Speed=}\frac{\text{Distance}}{\text{Time}}\] |
\[=\frac{16\pi r}{40}\,\,\text{m/}\min \] |
\[=\frac{2\pi r}{5}\,\,\text{m/}\min \] |
New circumference \[=2\pi r\times 10\pi =20\pi r\] |
\[\therefore \] Required time\[=\frac{20\pi r}{2\pi r}\times 5\min \] |
= 50 min |
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