SOLUTION: a boat travels 3km upstream and 3km back. the time for the round trip is 10 hours. the speed of the stream is 5 km/hr. what is the speed of the boat in still water

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Question 933065: a boat travels 3km upstream and 3km back. the time for the round trip is 10 hours. the speed of the stream is 5 km/hr. what is the speed of the boat in still water
Answer by ptfile(81) About Me  (Show Source):
You can put this solution on YOUR website!
Let 3km = the distance the boat traveled
5kph= the speed of the stream
a boat travels 3km upstream and 3km back. the time for the round trip is 10 hours. the speed of the stream is 5 km/hr.
Distance = (rate)(time)
time = Distance/rate
rate = Distance/time

3/(x+5) + 3/(x-5)=10
(3x-15 + 3x+15)/(x+5)(x-5)= 10
6x/(x+5)(x-5)=10
6x =10(x+5)(x-5)
6x =10 (x^2-25)
3x =5 (x^2-25)
3x =5x^2-125
0 =5x^2-3x-125
x+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+

x+=+%283+%2B-+sqrt%28+9%2B2500+%29%29%2F%2810%29+
x+=+%283+%2B-+sqrt%28+2509+%29%29%2F%2810%29+
x= 5.30899191454728 or 5
or
x= -4.70899191454728 or -5
The boat's speed is 5kph.