**Inlet: **A pipe connected with a tank or a cistern or a reservoir, that fills it, is known as an inlet.

**Outlet: **A pipe connected with a tank or a cistern or a reservoir, emptying it, is known as an outlet.

If a pipe can fill a tank in x hours, then: part filled in 1 hour = \(\frac{1}{x}\)

If a pipe can empty a full tank in y hours, then: part emptied in 1 hour = \(\frac{1}{y}\)

If a pipe can fill a tank in x hours and another pipe can empty the full tank in y hours (where y>x ) then on opening both the pipes, the net part filled in 1 hour = \(\left(\frac{1}{x}-\frac{1}{y}\right)\)

If a pipe can fill a tank in x hours and another pipe can empty the full tank in y hours (where x>y), then on opening, both the pipes, the net part emptied in 1 hour = \(\left(\frac{1}{y}-\frac{1}{x}\right)\)