Precalculus word problem!

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A hiker is one fourth  of the way through a narrow train tunnel when he looks over his shoulder and sees a train approaching the tunnel at 30mph. He quickly figures that if he runs in either direction at his top speed he can just make it out the tunnel. What is his top speed?

May 3rd, 2015

assume that the length of tunnel is L miles, the train is y mile from the end of tunnel,  and his top speed is x mph, then we have

y/30 = (L/4)/x ---> y = 7.5L/x 

(y+L)/30 = (3L/4)/x ---> y+L = 22.5L/x 

L = 15L/x 

x = 15 

 


May 3rd, 2015

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May 3rd, 2015
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