SOLUTION: An express train travels 150 miles in the same time a freight train goes 100 miles. Find their average speeds if the freight train travels 20 mph less than the express train

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Question 596396: An express train travels 150 miles in the same time a freight train goes 100 miles. Find their average speeds if the freight train travels 20 mph less than the express train
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
L:et +t+ = the same time for both trains in hours
Let +s+ = the speed of the express train in mi/hr
+s+-+20+ = the speed of the freight train in mi/hr
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Equation for express train:
(1) +150+=+s%2At+
Equation for freight train:
(2) +100+=+%28+s+-+20+%29%2At+
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(2) +100+=+s%2At+-+20t+
Substitute (1) into (2)
(2) +100+=+150+-+20t+
(2) +20t+=+150+-+100+
(2) +20t+=+50+
(2) +t+=+2.5+ hrs
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(1) +150+=+s%2At+
(1) +150+=+s%2A2.5+
(1) +s+=+150%2F2.5+
(1) +s+=+60+ mi/hr
and
(2) +100+=+%28+s+-+20+%29%2At+
(2) +100+=+%28+s+-+20+%29%2A2.5+
(2) +100+%2F+2.5+=+s+-+20+
(2) +s+-+20+=+40+
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The average speed of the express train in 60 mi/hr
The average speed of the freight train in 40 mi/hr