hhaekyoungp1sgbs
hhaekyoungp1sgbs hhaekyoungp1sgbs
  • 01-07-2018
  • Mathematics
contestada

Please help me with #25

Please help me with 25 class=

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sqdancefan
sqdancefan sqdancefan
  • 01-07-2018
time = distance/speed

Let b represent the speed of the boat in miles per hour. Then the speed upstream is b-3, and the speed downstream is b+3. The total time is
   4 = 20/(b-3) + 8/(b+3)
   4(b-3)(b+3) = 20(b+3) +8(b-3) . . . multiply by the product of the denominators
   4(b^2 -9) = 28b +36
   4b^2 -28b -72 = 0
   4(b-9)(b+2) = 0
   b = 9 or -2 . . . . . -2 is an extraneous solution

The speed of the boat in still water is 9 mph.
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