Question 884936
In 2.5 hours, the trains travel 255 miles.  255/2.5 = 102 miles per hour (combined speed).
A + B = 102
A = B + 20 [One train travels 20 miles faster than the other.]
Substitute the value of A from the second equation into the first.
A + B = 102
(B+20) + B = 102
Add
2B + 20 = 102
Subtract 20 from each side
2B = 82
Divide each side by 2
B = 41
If train B is traveling 41 mph, then train A is traveling 41+20, or 61 mph
.
Let's prove it.
Train A travels 61 mph for 2.5 hours.  61 * 2.5 = 152.5 miles
Train B travels 41 mph for 2.5 hours.  41 * 2.5 = 102.5 miles
Add them together: 152.5 + 102.5 = 255 miles