Question 169049
If two trains are 120 miles apart and are traveling toward each other at a constant rate of 30 mph and 40 mph respectively, how far apart will they be exactly 1 hour before they meet. 
----------------
Since they're approaching, their "closure rate", the rate at which they approach each other, is the sum of their speeds.
The approach each other at 30 + 40 mph, = 70 mph.
1 hour before converging, they'll be 70 miles apart.