Working together, pipes A and B can fill an empty tank in 10 hours. They worked together for 4 hours and then B stopped, and A continued filling the tank till it was full. It took a total of 13 hours to fill the tank. How long would it take A to fill the empty tank alone?

Question

Question

This question was previously asked in

RRB ALP Previous Paper 3 (Held On: 9 Aug 2018 Shift 3)

Answer 1

Calculation:

Working together, pipes A and B can fill an empty tank in 10 hours,

⇒ 1/A + 1/B = 1/10

together they worked for 4 hours and then A continued, and work completed in 13 hrs,

It means A worked for 13 hrs.

⇒ (4/A + 4/B) + 9/A = 1

⇒ 4/10 + 9/A = 1

∴ A = 15 hrs

Alternate Method

Time is taken to fill the tank by A and B = 10 hrs = 100% of total work

A and B worked together for 4 hrs = 40% of total work

So, 6 hours of work remaining = 60% of total work

Work done by A alone = 13 - 4 = 9 hours

60% of work is done by A in 9 hours

100% of work = (9/60) × 100 = 15 hours

∴ The time taken by A to complete work is 15 hours.