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Your must reach from point A to point B in 20 minutes. Distance between the two points in 9.95 miles. 3 miles from point A, there is a tunnel the length of the tunnel is 1.2 miles. Inside the tunnel, you can only go 15 mph and under. What is the average speed you must keep outside of the tunnel in order to reach from point A to point B in 20 minutes?

user50372
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    Figure out how long it will take you to get through the tunnel. Subtract that from 20 minutes. Figure out how long the above ground portion of the trip is. figure out how fast you have to go to complete the above ground trip in order to make it in the time you have left for the above ground trip. – Mitchell Kaplan Jun 12 '14 at 11:22
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    Hi. It would be good if you could give some indication of what you have already tried, so people can see where you are getting stuck – Joe Tait Jun 12 '14 at 11:34

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Length of tunnel = 1.2 miles. Maximum speed in tunnel = 15mph

If you maintain the maximum speed throughout the tunnel, then it will take 1.2/15 = 0.08 hrs (4.8 mts) to cross the tunnel.

So, time available to travel the remaining 8.75 miles = 15.2 mts

Required average speed outside the tunnel = 8.75 x 60 / 15.2 = 34.539 mph.

OC2PS
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