<PRE><B>Question 346237</B>
Rate*Time=Distance
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Average speed equals total distance divided by total time.
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For the first mile,
{{{10*t[1]=1}}}
{{{t[1]=1/10}}}
For the second mile,
{{{R*t[2]=1}}}
{{{t[2]=1/R}}}
The total distance is 2 miles.
The total time is {{{t[1]+t[2]=1/10+1/R}}}
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{{{2/(1/10+1/R)=20}}}
{{{2=20(1/10+1/R)}}}
{{{2=20/10+1/R}}}
{{{2=2+1/R}}}
{{{1/R=0}}}
There is no solution.
You cannot go fast enough to average 20 mph.
20 mph for a 2 mile track requires 1/10 hr. 
You already used that 1/10 hr for your first lap.
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