Originally Posted by

**M.R** I have done as advised. However i am not getting the correct answer?

So we have two equations:

$\displaystyle \frac {8}{L} + \frac {8}{S} = 1$

$\displaystyle S = L + 120$

$\displaystyle \frac {80}{L} + \frac{80}{L+80} = 1$ Mr F says: This line is wrong (and all that follows will be wrong). It should be $\displaystyle {\color{red}\frac {80}{L} + \frac{80}{L+{\color{blue}120}} = 1}$.

$\displaystyle (L+ 80) 80 + 80L = L(L+80)$

$\displaystyle 80L + 80*80 + 80L = L^2+80L$

$\displaystyle L^2-80L-6400 = 0$

Applying the quadratic formula we have

$\displaystyle L = \frac {80 + \sqrt {32000}}{2}$

Which is not the correct answer. The answer as given in the textbook is Large pipe 2 hours , small pipe 4 hours?