SOLUTION: The average speed of an express train is 15 mph faster than the average of a local train. It takes the local train 2 hours longer than the express train to cover 360 miles. What i

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Question 614334: The average speed of an express train is 15 mph faster than the average of a local train. It takes the local train 2 hours longer than the express train to cover 360 miles. What is the average speed of the express train?
Answer by lwsshak3(11628) About Me  (Show Source):
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The average speed of an express train is 15 mph faster than the average of a local train. It takes the local train 2 hours longer than the express train to cover 360 miles. What is the average speed of the express train?
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let x=speed of the local train
x+15=speed of express train
travel time=distance/speed
..
360/x-360/(x+15)=2
360(x+15)-360x=2x(x+15)=2x^2+30x
360x+5400-360x=2x^2+30x
2x^2+30x-5400=0
x^2+15x-2700=0
(x-45)(x+60)=0
x=-60(reject, x>0)
or
x=45
x+15=60
ans:
speed of express train=60 mph