<PRE><B>Question 393202</B>
Two pumps of different sizes working together can empty a tank in 3 hours.
 The larger pump can empty this tank in 5 hours.
 How long will it take the smaller one to do the job alone? 
:
Let t = time required by the small pump alone
:
Let the completed job = 1 (an empty tank)
:
Each pump will do a fraction of the job, the two fractions add up to 1
:
{{{3/5}}} + {{{3/t}}} = 1
Multiply by 5t, results
3t + 5(3) = 5t
:
15 = 5t - 3t
15 = 2t
t = {{{15/2}}}
t = 7.5 hrs, the small pump alone
;
:
Check the solution
{{{3/5}}} + {{{3/7.5}}} = 
.6 + .4 = 1; confirms our solution</PRE>