If two pipes function simultaneously, a tank is filled in 12 hours. On...
Using Rule 1,
If the slower pipe fills the tank in x hours, then

Required time = 30 - 10 = 20 hours
View all questions of this testIf two pipes function simultaneously, a tank is filled in 12 hours. On...
Understanding the Problem
To tackle the problem, let's define the variables and the relationships between the pipes.
- Let the time taken by the slower pipe to fill the tank be \( x \) hours.
- Then, the faster pipe will take \( x - 10 \) hours to fill the tank.
Working Together
When both pipes work together, they fill the tank in 12 hours. The rates of filling for each pipe are:
- Slower pipe: \( \frac{1}{x} \) (tank per hour)
- Faster pipe: \( \frac{1}{x - 10} \) (tank per hour)
The combined rate of both pipes working together is:
\[ \frac{1}{x} + \frac{1}{x - 10} = \frac{1}{12} \]
Setting Up the Equation
To find \( x \), we can combine the fractions:
\[ \frac{(x - 10) + x}{x(x - 10)} = \frac{1}{12} \]
This simplifies to:
\[ \frac{2x - 10}{x^2 - 10x} = \frac{1}{12} \]
Cross-multiplying gives:
\[ 12(2x - 10) = x^2 - 10x \]
Expanding and rearranging results in:
\[ x^2 - 34x + 120 = 0 \]
Solving the Quadratic Equation
Now, we can solve this quadratic equation using the quadratic formula:
\[ x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \]
Where \( a = 1, b = -34, c = 120 \):
- Discriminant: \( b^2 - 4ac = 1156 - 480 = 676 \)
- Roots:
\[ x = \frac{34 \pm 26}{2} \]
Calculating gives:
- \( x = 30 \) (slower pipe)
- \( x = 4 \) (not valid since it must be greater than 10)
Therefore, the slower pipe takes 30 hours, and the faster pipe takes:
\[ x - 10 = 30 - 10 = 20 \text{ hours} \]
Conclusion
The faster pipe alone takes 20 hours to fill the tank, confirming the correct answer is option B.