Question

Pipe A can fill a cistern in 6 hours and pipe B can fill it in 8 hours. Both the pipes are opened and after two hours, pipe A is closed. How much time will B take to fill the remaining part of the tank?

Answer 1

Part of the tank filled by pipe A and B in 2 hrs.

$=2(\frac{1}{6}+\frac{1}{8})=2\left(\frac{4+3}{24}\right)=\frac{7}{12}$

Remaining part $=1-\frac{7}{12}=\frac{5}{12},$ This part is filled by pipe B.

$\therefore$ Required time $=\frac{5}{12}\times 8=\frac{10}{3}=3\frac{1}{3}$ hrs.