Question 595536
Let time taken by hose A to fill the pool = A hrs
time taken by hose B = B hrs
and time taken by both hoses together  = C hrs 

According to the formula 
{{{1/A+1/B=1/C}}}

i.e. {{{1/3+1/B=1/2}}}
{{{1/B=1/2-1/3}}}
{{{1/B=(3-2)/6}}}
{{{1/B=1/6}}}

this means B = 6 hrs

So hose B takes 6 hours to fill the pool.