Question 1019723
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Suppose an average professor can do a certain job in nine hours and an average student can do the same job in 6 hours.  
If three professors and two students work together, how long will the job take?
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<pre>
The rate of each professor is {{{1/9}}} job-per-hour.

The rate of each student is {{{1/6}}} job-per-hour.

The rate of the tree professors and 2 students working simultaneously is

{{{3/9}}} + {{{2/6}}} = {{{(1+1)/3}}} {{{2/3}}} job-per-hour.

Hence, it will take {{{3/2}}} = {{{1}}}{{{1/2}}} an hour for three professors and two students to get the job complete if they work together.

<U>Answer</U>. In {{{1}}}{{{1/2}}} an hour.
</pre>

See the lesson <A HREF=http://www.algebra.com/algebra/homework/Rate-of-work-word-problems/Word-problems-WORKING-TOGETHER-by-Fractions.lesson>Using fractions to solve word problems on joint work</A> in this site for many other samples 
of solved problems on joint work.