Train A left Centerville station, heading towards Dale City Station, at 3PM. Train B left Dale City Station, heading toward Centerville Station, at 3:20PM on the same day. The trains rode on straight tracks that were parallel to each other. If Train A traveled at a constant speed of 30 miles per hour and Train B traveled at a constant speed of 10 miles per hour, and the distance between the Centerville Station and Dale City Station is 90 miles, when did the trains meet each other?
From 3 Pm to 3:20 PM , train A will have travelled a distance of 20/60 * 30 = 10 miles. So at 3:20 distance remaining between train A and train B =80 miles.
Now let train A and train B meet x hours after 3:20. In x hours both trains will have travelled a total distance of 80 kms.
so, 30 X + 10X = 80
40x =80. there X =2
so trains will meet each other at 5:20.