A cistern can be filled by an inlet in 6 hours and can be emptied by an outlet in 8 hours. If the inlet and outlet are opened together, in what time the cistern can be filled?

24 hours

The following chart has to be made first:

Efficiency of Inlet = 4

Efficiency of Outlet = -3

When Inlet and Outlet are opened together, efficiency = 4 - 3 = 1

Thus, it takes 24 hours to fill in the cistern = \(\frac{ 24}{1 }\) = 24 hours