Posted by solve this please. on .
Trains A and B are traveling in the same direction on parallel tracks. Train a is traveling at 100 mph and train B is traveling 120 mph. Train a passes a station at 7:20 P.M. If train B passes the same station at 7:35 P., at what time will train B catch up to train A?

math/algebra 
MathMate,
By 7:35, train A would have gone 15min. past the station. The distance travelled would have been 100 mph*15/60 hours = 25 miles.
Train B catches up at the rate of 120100 mph=20 mph. How long would it take to catch up? 
math/algebra 
Henry,
7:35 PM  7:20 PM = 15 min = 0.25 h,
When train B catches up with A, their
distance traveled will be equal. But A
traveled that distance in 15 min(0.25h)
less. Therefore:
d1 = d2,
100t = 120(t  0.25),
100t = 120t  30,
100t  120t = 30,
20t = 30,
t = 1.5 h = train A time traveled.
(t  0.25) = 1.5  0.25 = 1.25 h =
1:15 = Time needed for B to catchup,
B caughtup at: 7:35 PM + 1:15 = 8:50PM.