speed in still water ---- x
rate upstream = x-9 , where x is clearly > 9
rate downstream = x+9
17/(x+9) + 17/(x-9) = 13
times (x+)(x=9) or x^2 - 81
17(x-9) + 17(x+9) = 13(x^2 - 81)
17x - 153 + 17x + 153 = 13x^2 - 1053
13x^2 - 34x - 1053 = 0
x = (34 ± √55912)/26
= appr 10.4 or a negative which would make no sense.
the boat can go 10.4 mph in still water
The current in a stream moves at a speed of 9 mph. A boat travels 17 mi upstream and 17 mi downstream in a total time of 13 hrs. What is the speed of the boat in still water?
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1 answer