Question

In a well there is 800 liters of water. At the top there is a pipe that deposits 25 l per minute into the well, and at the bottom there is another pipe which withdraws 30 l per minute from the same well. How many liters of water will there be in the well after 15 minutes of the pipes functioning?

Answer 1

Water left after 1 min=(800+25)-30=825-30=795
therefore water left after 15 min=(800+25*15)-30*15=(800+375)-450=1175-450=725litres.
Hope i helped u:)

Answer 2

total amount of water in well after 1 min =25 - 30 = -5 = 5 

 after 15 min = 15*5 = 75 litre

total water 15 min = 800 - 75 =725