Question

Two pipes A and B can fill a tank in 24 minutes and 32 minutes respectively. If both the pipes are opened simultaneously, after how much time should B be closed so that the tank is full in 18 minutes

• A. 2 min
• B. 4 min
• C. 6 min
• D. 8 min

Answer 1

The correct option is D 8 min

Let the total capacity of the tank be 96 units (LCM of 24 & 32).
A fills = $\frac{96}{24}$ = 4 units / minute.
B fills = $\frac{96}{32}$ = 3 units / minute.
Let the time for which B is opened is x minutes.
According to the question, 4 $\times$ 18 + 3 $\times$ x = 96
3x = 96 - 72 = $\Rightarrow$ 3x = 24
x = 8 minutes.
The pipe B should be closed after 8 minutes.