Question

two pumps can fill a water tank in 20 minutes and 15 minutes individually. an out let can empty the full tank in 30 minutes, if the out let is forgotten to be closed and pumps are switched in how many time do all of them fill the tank​

Answer 1

Explanation:

$\frac{1}{20} + \frac{1}{15} = \frac{7}{60} - \frac{1}{30} = \frac{5}{60} = \frac{60}{5} = 12 \: mnuts \: \:$