Question 497611
Pump A can fill up an empty pool in 6 hours.
 Pump B can fill up the same empty pool in 12 hours.
 If the pool is already 1/3 full, how long will it take for both of the pumps
 working together to fill up the remainder of the pool?
:
Let t = time to complete filling the pool by both Pumps
Let a full pool = 1, then the amt remaining to be filled = {{{2/3}}}
:
{{{t/6}}} + {{{t/12}}} = {{{2/3}}} 
multiply equation by 12
12*{{{t/6}}} + 12*{{{t/12}}} = 12*{{{2/3}}}
cancel the denominators and you have
2t + t = 4(2)
3t = 8
t = {{{8/3}}}
t = 2{{{2/3}}} hrs to complete filling the pool by both pumps