Question 1097855
<br>Here is an alternative method that I see many students preferring over the method shown in the two previous responses.<br>
(1) Multiply the times it takes the two of them alone to do the job: {{{2.5*4 = 10}}}<br>
In 10 hours, Bob could paint 2.5 of those fences, and Sarah could paint 4 of them.  So in 10 hours the 2 of them together could paint 6.5 fences.<br>
Then the number of hours they would need together to paint the one fence is {{{10/6.5 = 20/13}}}