SOLUTION: A boat traveled 315 miles downstream and back. Downstream took 15 hours and going back took 35 hours. What is the boat speed in still water and what is the speed of the current?

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Question 841990: A boat traveled 315 miles downstream and back. Downstream took 15 hours and going back took 35 hours. What is the boat speed in still water and what is the speed of the current?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +s+ = the boat's speed in still water
Let +c+ = the speed of the current
---------------------------------
Equation for going downstream:
(1) +315+=+%28+s+%2B+c+%29%2A15+
Equation for going upstream:
(2) +315+=+%28+s+-+c+%29%2A35+
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(1) +s+%2B+c+=+315%2F15+
(1) +s+%2B+c+=+21+
and
(2) +s+-+c+=+315%2F35+
(2) +s+-+c+=+9+
--------------------
Add (1) and (2)
(1) +s+%2B+c+=+21+
(2) +s+-+c+=+9+
+2s+=+30+
+s+=+15+
and
(2) +s+-+c+=+9+
(2) +15+-+c+=+9+
(2) +c+=+15+-+9+
(2) +c+=+6+
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The boat's speed in still water is 15 mi/hr
The speed of the current is 6 mi/hr