A tank can be filled in 5 hrs by three pipes A, B and C. The pipe C is twice as fast as B and pipe B is twice as fast as. How much time pipe A alone will take to fill the tank ?

35 hrs

The correct answer is Option (2) → 35 hrs

Rate of Pipe A = $\frac{1}{x}$

Rate of Pipe B = $\frac{2}{x}$

Rate of Pipe C = $\frac{4}{x}$

$⇒\frac{1}{x}+\frac{2}{x}+\frac{4}{x}=\frac{1}{5}$

$⇒\frac{7}{x}=\frac{1}{5}$

$⇒x=35\, hrs$