Question 1140666
d/2, first half distance
d/2, second half distance
d, entire trip one-way
r, average speed for second half of trip

<pre>
              SPEED    TIME       DISTANCE

First Half       20      d/40       d/2

Second Half      r       d/(2r)     d/2

Totals                d/40+d/(2r)    d 
</pre>
Average Speed for d given as 40 miles per hour:

{{{highlight_green(d/(d/40+d/(2r))=40)}}}

Simplify that and <i>TRY</i> to solve for d.


{{{1/(1/40+2/(2r))=40}}}


{{{(80r)/(2r+40)=40}}}


{{{40(r+20)=40r}}}


{{{40r+800=40r}}}


{{{800=0}}}------<b>IMPOSSIBLE</b>

<b>NO SOLUTION</b>