An old puzzle -- Xiggi's Formula? Maybe...

[xiggi]

<p>

i believe the answer is 90 mph? 30+90 = 120/2 = 60 average.

</p>

<p>2.30.90 / 30+90 =
2.30.90 / 120 =
90/2 = 45 </p>

<p>:)</p>