Two bullet trains leave the station at the same time traveling in opposite direction. The northbound train goes 125 mph and the southbound train goes 120 mph. After how long will they be 735 miles apart?

Answer 1

distance=relative velocity*time
735=(125+120)t
solve for t.

Answer 2

Let the time traveled by each one be t hrs
distance gone by first = 125t miles
distance gone by 2nd = 120t miles

125t + 120t = 735
245t = 735
t = 3

After 3 hrs, they will be 735 miles apart