A can go round a circular path 8 times in 40 minutes. If the diameter of the circle is increased to 10 times the original diameter, then the time required by A to go round the new path once, travelling at the same speed as before, is :
Options:
A . 20 min
B . 25 min
C . 50 min
D . 100 min
Answer: Option C Let original diameter be d metre Then, its circumference = $$\left( {\pi d} \right)$$ metres Time taken to cover $$\left( {8\pi d} \right)$$ m = 40 min New diameter = $$\left( {10d} \right)$$ m Then, its circumference = $$\left( {\pi \times 10d} \right)$$ m ∴ Time taken to go round it once : $$\eqalign{ & = \left( {\frac{{40}}{{8\pi d}} \times 10\pi d} \right)\min \cr & = 50\,\min \cr} $$
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