Flow rate and proportion

Question

I'm wondering if there is a short cut for calculating the time taken for 2taps to fill and another tap to empty a tank apart from the usual way. For e g. two taps take 20minutes to for fill a tank while another 30minutes to empty the tank .Calculate the time taken to fill the tank .please help with short cut

Answer 1

The filling rate is the difference in the flow rates. Input rate $(\frac{V}{20})$/min - output rate $(\frac{V}{30})$/min $= (\frac{V}{60})$/minute where $V$ is the volume of the tank. So the time taken will be 60 minutes.