ANSWER:
Both the trains are 375 miles apart after 3 hours of journey.
SOLUTION:
Given, two trains leave Chicago at the same time in different directions,
Let the two trains be train A, train B.
And speed of train A is 60 miles per hour
Speed of train B is 65 miles per hour
We need to find time after which distance between two trains becomes 375 miles.
Let the time at which they are 375 miles apart be "t",
And distance traveled by A be "x", then distance traveled becomes 375 – x.
We know that, distance traveled = speed
time
For train A:
x = 60t --- eqn (1)
For train B :
375 – x = 65t -- eqn 2
Substitute (1) in (2)
375 – 60t = 65t
375 = 65t + 60t
125t = 375
t = 3
hence, both the trains are 375 miles apart after 3 hours of journey.