Question 1064380
Jason and Hilger are required to paint over the graffiti on a wall. 
If Jason worked alone, it would take him 20 hrs to repaint.  Working
alone, Hilger could do the job in 15 hrs.  How long will it take them 
to do the painting If they work together? 
<pre>

Jason's working rate is 1 job in 20 hrs or 1/20 jobs per hour.
Hilger's working rate is 1 job in 15 hrs or 1/15 jobs per hour.

Their combined rate = 1/20 + 1/15 = 3/60 + 4/60 = 7/60 jobs per hour.

(Number of jobs done) = (rate in number of jobs per hour) × (number of hours)

Number of jobs done = 1 job
Rate in number of jobs per hour = 7/60
Number of hours = x

(Number of jobs done) = (rate in number of jobs per hour) × (number of hours

                    1 = (7/60)(x)

Multiply both sides by 60 and solve for x

Edwin</pre>