A rectangular water tank is 80 m $$x\times$$ 40 m. Water flows into it through a pipe of 40 sq.cm at the opening at a speed of 10 km/hr. The water level will rise in the tank in half an hour is

given rectangular water tank is 80 m $$x\times$$ 40 m

volume of rectangular water tank = volume of water filled by the pipe (area of pipe $$\times$$ speed of flow of water)

volume of rectangular water tank = 8000 $$x\times$$ 4000 {$$\because$$ 80 m = 8000 cm , 40 m = 4000 cm}

 8000 $$x\times$$ 4000 = 40 $$\times 10 \times 1000 \times 100$$ {$$ 1 km = 1000 m , 1 m =100 cm$$}

x = $$\frac{10}{8}$$ { height raised in 1 hr}

height raised in 30 mins = $$\frac{5}{8}$$