Question

One pump can fill a tank with oil in 10 hours. Together with a second pump, it can fill the tank in 6 hours. How long will it take the second pump to fill the tank if it is used alone?

Answer 1

Answer:

The second pump can fill a tank with oil in 15 hours.

Step-by-step explanation:

It is given that one pump can fill a tank with oil in 10 hours. Together with a second pump, it can fill the tank in 6 hours.

Let the second pump can fill a tank with oil in t hours.

One hour work of first pump is $\frac{1}{10}$.

One hour work of second pump is $\frac{1}{t}$.

One hour work of both pump together is $\frac{1}{6}$.

1 hour work of both = 1 hour work of 1st pump + 1 hour work of 2nd pump

$\frac{1}{6}=\frac{1}{10}+\frac{1}{t}$

$\frac{1}{6}=\frac{t+10}{10t}$

Cross multiply.

$10t=6(t+10)$

$10t=6t+60$

Subtract 6t from both the sides.

$10t-6t=60$

$4t=60$

Divide both the sides by 4.

$t=15$

Therefore the second pump can fill a tank with oil in 15 hours.

Answer 2

Answer:

The first pump can do 1/0 of the work per hour  

Together they do 1/6 of the work per hour  

The second alone would do (1/6 - 1/10) of the work per hour.  

1/6 - 1/10 = 1/15  

The second pump would take 15 hours to do the work.  

C) 15

Hope this helps. :)