• # question_answer A cistern has two pipes. One can fill it with water in 8 h and the other can empty it in 5 h. In how many hours will the cistern be emptied if both the pipes are opened together when$\frac{3}{4}$of the cistern is already full of water? A) $3\frac{1}{3}$h                        B)  6 h C)  10 h                 D)  $13\frac{1}{3}$h

Net part emptied by both in 1 $h=\left( \frac{1}{5}-\frac{1}{8} \right)=\frac{3}{40}$ $\frac{3}{40}$part is emptied in 1h. $\frac{3}{4}$part will be emptied in$\left( \frac{40}{3}\times \frac{3}{4} \right)\,\,h=10\,\,h$