Two trains are 500 miles apart when they first enter a collision course. If, after two hours, the distance between them is 300 miles and one train goes 20 mph faster than the other, find the speed of the faster train.

60 miles per hour. In two miles the sum of the distance the two trains traveled was 200 miles, you divide that by 2, the sum of the speed of the two trains is 100 miles per hour, now put the speed of the slow train as  x and the fast as x +20, the sum of x and x +20 is 100, so 2x + 20 =100, you subtract 20 from both sides, 2x = 80, divide by 2, x = 40, the problem asks for the speed of the fast train, so, x + 20 is 60.