Question

A tank has two pipes A and B. A can fill the tank with water in 8 hours and B can empty it in 12 hours. If the pipe A be opened first and the pipes be opened alternatively one at a time for 1 hour each, in how many hours will the tank be filled up?

Answer 1

Pipe A alone can fill the tank = 8 hrs

Pipe B alone can fill the tank = 12 hrs

Time ratio of Pipe A and B = 8 ∶ 12 = 2 ∶ 3

Concept used:

Efficiency is inversely proportional to time.

Answer 2

Answer:

9 1/2

Step-by-step explanation:

pipe A alone can feel the tank = 8 hour

pipe B alone can fill the tank = 12 hours

time ratio A and B = 8 : 12 = 2:3

efficiency is inversely proportional to time

efficiency of ratio a and b = 3 : 2

total work 3×8 = 24 both pipe open alternately for 1 hour

total work in 2 hours = 3+2 = 5

work in 8 hours = 5 × 4 = 20

work in next hour (9 th) = 20 + 3 = 23

remaining work = 24 - 23 = 1

B alone can work in 1 hour = 2

B alone can work in 1/2 hr = 1

so , the total work completes in 91/2 hours ( in 9 half hours)

Hope it helps