Question 466974
<pre>
The trains are approaching each other at a rate of
60+70 or 130 mph. [That's how fast the original 
65 mile distance between them is shrinking.] Since 
time = distance/rate, the trains will collide in 
65/130 hours which reduces to 1/2 hour.  During that 
half hour, the fly, traveling at 110 mph, will have 
flown half of 110 miles or 55 miles.

Edwin</pre>