Question

Pipe A can fill a tank three times faster than Pipe B. If together the two pipes can fill the tank in 36 minutes, then Pipe B alone will be able to fill the tank in

• A. 81 minutes
• B. 108 minutes
• C. 144 minutes
• D. 192 minutes

Hint:

If one pipe is $n$ times faster → its rate is $n$ times Always work with rates, not time directly.

Answer 1

The Correct Option is C

Concept: Work rates: \[ \text{Rate} = \frac{1}{\text{Time}} \]

Step 1: Assume rate of Pipe B.
Let Pipe B fills $\frac{1}{x}$ tank per minute. Then Pipe A (3 times faster): \[ \frac{3}{x} \]

Step 2: Combined rate.
\[ \frac{1}{x} + \frac{3}{x} = \frac{4}{x} \] Given: \[ \frac{4}{x} = \frac{1}{36} \]

Step 3: Solve for $x$.
\[ x = 144 \]

Step 4: Final conclusion.
Thus, Pipe B alone fills the tank in: \[ 144 minutes \]