Question

Water is pouring into a tank at a constant rate. When the tank is full, 10 pumps of equal capacity empty the tank in 12 hrs, while 15 pumps of the same capacity empty the tank in 6 hrs. The time which 25 pumps of the same capacity take to empty the tank, if the tank is initially full, will be : (All the pipes pouring water into the tank are always open)?

Answer 1

let x be the rate of the water pouring in
let y be the rate of one pump
120y-12x=1
90y-6x=1
solve for x, y
30y=6x
y=x/5
x=1/12
y=1/60
then sub
25yt-xt=1 to solve for t
5t/12- t/12=1
t=3hours