Water in a rectangular reservoir having base 80 m by 60 m is 6.5 m deep. In what time can the water be emptied by a pipe of which the cross-section is a square of side 20 cm, if the water runs through the pipe at the rate of 15 km/hr.
Given,
Dimension of rectangular reservoir = 80m×60m
Depth of water in reservoir = 6.5 m
Side of square pipe = 20cm
Rate of flow of water through pipe = 15 km/h
Volume of reservoir = 80×60×6.5 m3
Volume of pipe = 
Let reservoir be emptied in t hours
= 
= t =
24