It takes one pipe x minutes, the other pipe x+3 minutes
the portion filled per minute is by one pipe is 1/x, by the second pipe 1/(x+3)
when two pipes running together:
3&1/3[1/x+1/(x+3)] =1, 1 means the whole cistern
solve for x: 3&1/3(x+3) +3 1/3(x)=x(x+3)
6 &2/3 x +10 =x^2+3x
x^2- (3&2/3) x-10=0
3x^2-11x-30=0
this cannot be factored, so use the quadratic equation:
x is about 5.5
x+3=8.5
