Question

A train moving at 60 mph leaves the station at noon. An hour later , a train moving 80 mph leaves heading the same direction on a parallel track. Find the time when the second train catch up to the first.

Answer 1

4 pm

Explanation:

We are looking for the time it takes for both trains to travel the same distance.

distance = unknown, but it is the same for both trains

train 1: speed = s = 60 mph, time = t, distance = d

train 2: speed = s = 80 mph, time = t - 1, distance = d

speed = distance/time

distance = speed * time

Train 1:

d = 60t

Train 2:

d = 80(t - 1)

The distances, d, are the same, so

80(t - 1) = 60t

80t - 80 = 60t

20t = 80

t = 4

It takes 4 hours after the first train leaves for the second train to catch up to it, so the second train catches up to the first train at 4 pm.

Answer: 4 pm