Question 1089300
<pre>
               SPEED        TIME         DISTANCE
RAIN            r           252/r         252
NO RAIN         r+4         240/(r+4)     240
Total                        13
</pre>

{{{252/r+240/(r+4)=13}}}

-

{{{252(r+4)+240r=13*r(r+4)}}}
.
.
{{{13r^2-440r-1008=0}}}


discriminant, {{{440^2+4*13*1008=246016=496^2}}}


{{{highlight_green(r=(440+496)/(2*13)=highlight(36))}}}