Question 1206703
Allen can do a job 5 times faster than Billy. 
Billy can do the same job in 8 hours. 
How long will it take to do it together?
<pre>

Here's the LCM method:

The LCM of the given numbers 5 and 8 is 40.</pre>Billy can do the same job in 8 hours.<pre>So Billy can do 5 jobs in 40 hours.</pre>Allen can do a job 5 times faster than Billy.<pre>So Allen can do 25 jobs in 40 hours.

So together they can do 30 jobs in 40 hours.

So together they can do 1 job in 40/30 hours, 

or 1 1/3 hours or 1 hour and 20 minutes.

Edwin</pre>