Question

A can go round a circular path 8 times in 40 min- utes. If the diameter of the circle is increased to 10 times the original diameter, the time required by A to go round the new part once, travelling at the same speed as before is 1. 25 min. 2. 20 min. 3. 50 min. 4. 100 min.​

Answer 1

50 min.

Step by Step

$\bold{Circumference = 2\pi \: r}$

Distance covered in 1 min

$= 2 \times \frac{8}{40} \times \pi \:r$

New circumference

$=2×π×r×10$

Time taken

$\bold{ = \frac{2πr×10×40}{2πr×8} = 50 \: min}$