1st and 2nd pipe: X hours.
1st pipe: x+9 hours.
2nd pipe: (x+9) +7 = x+16.
1/(x+9) +1/(x+16) = 1/x
(x+16)/(x+9)(x+16) + (x+9)/(x+9)(x+16) = 1/x
(2x+25)/(x+9)(x+16) = 1/x
(x+9)(x+16) = 2x^2+25x
x^2+16x+9x+144 = 2x^2+25x
x^2 = 144
X = 12 hours.
It takes the first pipe 9 more hours to fill the pool than the first and the second pipes together and 7 less hours than it would take the second pipe if it was working alone. How long would it take to fill up the pool if both pipes were working together?
1 answer