A pipe of diameter 'd' can drain a water tank in 40 minutes. The time taken by a pipe of diameter '2d' for doing the same job is:
Answer & explanation
Correct answer: option 2
Note: Ratio of efficiency of the pipes is always equal to the square of the radius of the pipes.
I : II
Diameter : D : 2D
Radius : 1 : 2
Efficiency: 12 : 22
Time : 4 : 1
Here,
4R = 40 min,
1R = 10 min.