Question

An empty tank is filled using 5 pipes in 60 minutes. How many more same type of pipes are needed if the tank is to be filled in 30 minutes?

• A. 5
• B. 7.5
• C. 10
• D. 12

Answer 1

The correct option is A 5

5 pipes are required to fill a tank in 60 minutes

Let the number of pipes required to fill a tank in 30 minutes be x

Total number of pipes needed to fill the tank in 30 min = x + 5

Time taken to fill the tank by (x+5) pipes = 30 minutes

As the tank needs to be filled faster(less time) more number of pipes will be required. Hence the number of pipes and time taken to fill the tank is in inverse proportion.

$\Rightarrow \frac{\text{Number of pipes intially used}}{\text{Total number of pipes to fill the tank in 30 min}}=\frac{\text{Time taken to fill the tank by x+5 pipes}}{\text{Time taken to fill the pipe by 5 pipes}}$
$\Rightarrow$ $\frac{5}{x+5}=\frac{30}{60}=\frac{1}{2}$
Solving by cross-multiplication,

$\Rightarrow 5\times 2=1\times (x+5)$

$\Rightarrow 10=x+5$
Subtract 5 from both the sides
$\Rightarrow 10-5=x+5-5$
$\Rightarrow$ $x=5$
Hence, 5 more pipes are required to fill the tank in 30 min.