SOLUTION: A bicyclist is riding at a speed of 18 miles per hour down a long hill. The distance D she travels in feet can be modeled by d(t)=4t^2+18t, where t is the time in seconds. How lon

Question 955035: A bicyclist is riding at a speed of 18 miles per hour down a long hill. The distance D she travels in feet can be modeled by d(t)=4t^2+18t, where t is the time in seconds. How long will it take her to reach the bottom of a 400 foot long hill?
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
A bicyclist is riding at a speed of 18 miles per hour down a long hill. The distance D she travels in feet can be modeled by d(t)=4t^2+18t, where t is the time in seconds. How long will it take her to reach the bottom of a 400 foot long hill?
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Solve::
4t^2 + 18t = 400
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2t^2 + 9t - 200 = 0
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(2t+25)(t-8) = 0
Ans: t = 8 seconds
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Cheers,
Stan H.
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