Distance between trains

One train runs from A to B at 105 miles per hour; the other runs from B to A at 85 miles per hour. How far apart were the two trains 30 minutes prior to their crossing?

Solution:

Two trains are 95 miles apart 1/2 Hr before they crossed each other

Relative Speed of the trains = 85+105 = 190MPH

One hour before they crossed, they would have been 190 miles apart.

Distance between the trains 1/2 hr before they crossed would be 190/2 = 95miles