Question

A train leaves a train station at 1 pm. It travels at speed of 60 mph. Another train leaves the same station an hour later and goes the same direction at a speed of 80 mph. In how many hours will the second train catch up with the first train?

Answer 1

Should be 3 hrs. when the second train leaves,it is 60 miles away from the first train and the speed difference is 80-60=20MPH, so it takes 60/20 hrs to catch up

Answer 2

Relationship between distance-velocity-time as following
d = vt

The second train will catch up on the same distance as the first train.
d₁ = d₂

The first train left one hour before the the second train, that means the first time has an hour more in running time.
t₁ = t₂ + 1

Now plug in the numbers
d₁ = d₂
v₁t₁ = v₂t₂
60t₁ = 80t₂
60(t₂ + 1) = 80t₂
60t₂ + 60 = 80t₂
60t₂ - 80t₂ = -60
-20t₂ = -60
t₂ = -60/-20
t₂ = 3
After 3 hours running, the second train will catch up with the first train.

Answer: 3 hours