A tank is filled in 10 hours by three pipes A, B and C. The pipe C is twice as fast as B and B is twice as fast as A. How much time will pipe A alone take to fill the tank?
70 hours
30 hours
35 hours
50 hours
Explanation:
Suppose pipe A alone takes x hours to fill the tank.
Then, pipes B and C will take $\dfrac{x}{2}$ and $\dfrac{x}{4}$ hours respectively to fill the tank.
$\therefore \dfrac{1}{x}+\dfrac{2}{x}+\dfrac{3}{x}=\dfrac{1}{10}$
$\dfrac{7}{x}=\dfrac{1}{10}$
x=70