SOLUTION: My question is: An express train leaves Chicago for Atlanta at 100 mph. At the same time a freight train leaves Atlanta for Chicago at 80 mph. If the distance between the two citie

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Question 670459: My question is: An express train leaves Chicago for Atlanta at 100 mph. At the same time a freight train leaves Atlanta for Chicago at 80 mph. If the distance between the two cities is 720 miles, how long will it take the trains to pass each other?
So far, I have:
C A
d=rt d=rt
d= 100t d=80t.
Im stuck on what to do next, please help??
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +d+ = distance C-A train travels
+720+-+d+ = distance A-C train travels
Let +t+ = the time that both travel until they meet
-----------
C-A train:
(1) +d+=+100t+
A-C train:
(2) +720+-+d+=+80t+
-------------------
Substitute (1) into (2)
(2) +720+-+100t+=+80t+
(2) +180t+=+720+
(2) +t+=+720%2F180+
(2) +t+=+4+
The trains will meet in 4 hrs
check:
(1) +d+=+100t+
(1) +d+=+100%2A4+
(1) +d+=+400+
and
(2) +720+-+d+=+80t+
(2) +720+-+400+=+80t+
(2) +320+=+80t+
(2) +t+=+320%2F80+
(2) +t+=+4+ hrs
OK