Question 211575
Two pipes are used to fill a water storage tank. 
The first pipe can fill the tank in 4 hrs, and the two pipes together can fill
 the tank in 2 hrs less time than the second pipe alone.
 How long would it take for the second pipe to fill the tank
:
Let t = time for the 2nd pipe to fill it alone
then
(t-2) = two hrs less
:
Let the completed job (full tank) = 1
:
{{{(t-2)/4}}} + {{{(t-2)/t}}} = 1
Multiply equation by 4t, results:
t(t-2) + 4(t-2) = 4t
:
t^2 - 2t + 4t - 8 = 4t
:
Arrange as a quadratic equation:
t^2 - 2t + 4t - 4t - 8 = 0
:
t^2 - 2t - 8 = 0
Factor
(t-4)(t+2) = 0
Positive solution:
t = 4 hrs is 2nd pipe time alone
:
:
Check solution in  original equation
{{{(4-2)/4}}} + {{{(4-2)/4}}} = 1
{{{2/4}}} + {{{2/4}}} = 1