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 = ^{1}/_{x}

If a pipe can empty a full tank in y hours,' then :
part emptied in 1 hour = ^{1}/_{y}

If a pipe can -fill a tank in i 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
= ^{1}/_{x} - ^{1}/_{y}

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
= ^{1}/_{y} - ^{1}/_{x}