Question

pipe a can fill a tank in 14 minutes pipe b can fill it in 7 minutes and pipe C can empty full tank in 28 minutes if all them are opened simultanelously find the time taken to fill the empty tank

Answer 1

$\frac{1}{time} = \frac{1}{14} + \frac{ 1}{7} - \frac{1}{28} \\ = \frac{2 + 4 - 1}{28} \\ = \frac{5}{28} \\ so \: time = \frac{28}{5} = 5.6minutes$