Question 925866
Pipe A can fill a tank in 25 minutes.
 Pipe B can fill the same tank in 20 minutes.
 To fill the empty tank, pipe A was opened alone for 3 minutes, and, after that, pipe B was also opened.
 How much time will it take for both pipes, A and B to finish filling the tank?
:
let t = for A & B to finish filling the tank
let the completed job = 1 (a full tank)
:
A shared work equation
{{{((t+3))/25}}} + {{{t/20}}} - 1
multiply equation by 100, cancel the denominators
4(t+3) + 5t = 100
4t + 12 + 5t = 100
4t + 5t = 100 - 12
9t = 88
t = 9.78 minutes for A & B to finish filling the tank