SOLUTION: Two trains leave a city on parallel tracks,traveling the same direction. The passenger train is going twice as fast as the freight train. After 45 minutes, the trains are 30 miles

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Question 420155: Two trains leave a city on parallel tracks,traveling the same direction. The passenger train is going twice as fast as the freight train. After 45 minutes, the trains are 30 miles apart. Find the speed of each train.
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Write an equation for both trains
Let s = speed of freight train
passenger train
(1) d%2B+30+=+2s%2A%283%2F4%29
freight train
(2) d+=+s%2A%283%2F4%29
------------------
Substitute (2) into (1)
(1) %283%2F4%29%2As++%2B+30+=+%283%2F4%29%2A2s
(1) 3s+%2B+120+=+6s
(1) 3s+=+120
(1) s+=+40
and
2s+=+80
the speed of the passenger train is 80 mi/hr
the speed of the freight train is 40 mi/hr
check:
(1) d%2B+30+=+80%2A%283%2F4%29
(1) d+=+60+-+30
d+=+30 mi
and
(2) d+=+40%2A%283%2F4%29
d+=+30 mi
OK