Question 146759
It's obvious you can't add the times, since 2 working would take less time.  You have to look at the inverse.
Edgar can do 1 walk/2 hours, and Ellen can do 1 walk/8 hours.  Add 1/2 and 1/8 to get 5/8.  Then invert that, = 8/5.
Together it takes 1.6 hours, less than either of them separately.  (Unless they yak too much, or spend time not working.)