SOLUTION: A Mississippi riverboat can travel 70 kilometers downstream in 5 hours and can make the return trip in 7 hours. Find the speed of the boat in still water.

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Question 689006: A Mississippi riverboat can travel 70 kilometers downstream in 5 hours and can make the return trip in 7 hours. Find the speed of the boat in still water.
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +s+ = the speed of the boat in still water
Let +c+ = the speed of the current
given:
(1) +s+%2B+c+=+70%2F5+
(2) +s+-+c+=+70%2F7+
------------------
Add the equations
(1) +s+%2B+c+=+70%2F5+
(2) +s+-+c+=+70%2F7+
+2s+=+70%2F5+%2B+70%2F7+
+2s+=+%28+7%2A70+%29+%2F+35+%2B+%28+5%2A70+%29+%2F+35+
+2s+=+490+%2F+35+%2B+350+%2F+35+
+2s+=+840+%2F+35+
+s+=+420+%2F+35+
+s+=+12+
The speed of the boat in still water is 12 km/hr