Question 284297
<pre>
Let Desi's speed be R, then Fred's speed is then R-0.5
Their speed of separation is the sum of their speeds or R+R-0.5 or 2R-0.5
From 9:00 am to 1:00 pm is 4 hours.
Distance = Rate x Time
      20 = (2R-0.5)T
      20 = (2R-0.5)(4) 
      20 = 8R-2
      22 = 8R
    22/8 = R
    2.75 = R

Answer: Desi's speed of walking is 2.75 mph

Edwin</pre>