A water tank can be filled by two pipes A and B in 60 minutes and 40 minutes respectively. How many minutes will it take to fill the tank from empty state if B is used for half the time, and A and B fill it together for the other half?

A 30minutes

B 40 minutes

C 42minutes

D 57minutes

Solution

Correct Answer: Option A

Let the total time be x mins. Part filled in first half means in x/2 = 1/40 Part filled in second half means in x/2 = (1/60 + 1/40) = 1/24

Now, (x/2 * 1/40) + (x/2 + 1/24) = 1

x/2 * (1/40 + 1/24) = 1

x/2 * 1/15 = 1

x = 30 mins

Solution

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