Question 1131120
r, the normal speed

r+10, the "if increase by 10 kilometer/hour" speed


<pre>
                     SPEED       TIME       DISTANCE

Normal               r          200/r       200

If faster            r+10      200/(r+10)   200

Difference                      2/3
</pre>

The equation to match the time difference for 40 minutes, {{{2/3}}} of an hour,

{{{200/r-200/(r+10)=2/3}}}