This is a problem from the Jubilee Academy\'s online homeschooling website, whic

Question

This is a problem from the Jubilee Academy's online homeschooling website, which I am enrolled in.
A freight train leaves a station traveling a constant speed of 30 miles per hour (mph). A passenger train leaves at the same time and travels in the same direction at a constant speed of 35 mph. In how many hours will the trains be 15 miles apart?
I would be able to do this problem easily if i knew how to set up the equation, which is for me the hardest part, but there were no similar solvers in the travel and distance section. Thank you.

Explanation / Answer

Remember that x = Vt,,, where x is distance, V is velocity, and t is time
.
delta x = V2t2 - V1t1
.
but t1 = t2
.
delta x = (v2-v1) t
.
15 mi = ( 35 -30 ) mph * t
.
15 = 5 t
.
t=3 hrs
.
check
.
V2 = 35 *3 = 105 miles
.
V1 = 30 * 3 = 90
.
v2 -v1 =15 ok   

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