Question

Q48. A tank can be filled with water by two pipes A and B together in 36 minutes. If the pipe B was stopped after 30 minutes, the tank is filled in 40 minutes. The pipe B can alone fill the tank in

• A. (a) 45 minutes
• B. (b) 60 minutes
• C. (c) 75 minutes
• D. (d) 90 minutes

Answer 1

The correct option is

D

(d) 90 minutes

A tank can be filled with water by two pipes A and B together in 36 minutes.

Let pipe B fill the tank in x minutes

Part of the tank filled by pipes A and B in 1 minutes = $\frac{1}{36}$

Pat of the tank filled by pipe A in 1 minutes = $\frac{1}{36}-\frac{1}{x}$

30 $\frac{1}{x}$ + 40 ($\frac{1}{36}-\frac{1}{x}$) = 1

$\frac{30}{x}$ + ($\frac{40}{36}-\frac{40}{x}$) = 1

Solving for x we get:

$\frac{30}{x}$ + $\frac{10}{9}-\frac{40}{x}$ = 1

$\frac{10}{x}$ = $\frac{1}{9}$

x = 90 minutes.