SOLUTION: A boat travels 12 km upstream and back in 1 hour 45 minutes. If the speed of the current is 3 km/h throughout, find the speed of the boat in still water, giving your answer correc

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Question 400070: A boat travels 12 km upstream and back in 1 hour 45 minutes. If the speed of the current is 3 km/h throughout, find the speed of the boat in still water, giving your answer correct to 3 significant figures.
Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!


Hi

Let s represent the speed of the boat in still water

D = r*t  OR t = D/r

Question states*** (note round trip took 1.75hr)

 12/(s+3) + 12/(s-3) = 1.75hr

Solving for x

 12(s-3) + 12(s+3) = 1.75(s+3)(s-3)

    24s = 7/4(s^2-9)

     7/4s^2 - 24s - 63/4 = 0

       7s^2 - 96s - 63 = 0

s+=+%2896+%2B-+sqrt%2810980%29%29%2F%2814%29+  |discarding the negative solution

 s = 14.342 kmph