SOLUTION: A river flows at 2 m/s. What is the speed through the water of the boat that can go twice as fast downstream as upstream?

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Question 772699: A river flows at 2 m/s. What is the speed through the water of the boat that can go twice as fast downstream as upstream?
Found 2 solutions by josmiceli, josgarithmetic:
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 ( no current )
+s+%2B+2+ = speed of boat going downstream
+s+-+2+ = speed of boat going upstream
-----------------
given:
+s+%2B+2+=+2%2A%28+s+-+2+%29+
+s+%2B+2+=+2s+-+4+
+s+=+6+
6 m/s is the speed of the boat without current

Answer by josgarithmetic(39620) About Me  (Show Source):
You can put this solution on YOUR website!
A data table is not necessary and would be adding more details than we can use.
r = speed of boat if in still water
2 m/s = the given speed of the river's current

r+2 = downstream speed for boat in river
r-2 = upstream speed for boat in river

"twice as fast downstream as upstream":
Means that downstream speed is 2 times the upstream speed.
highlight%28r%2B2=2%28r-2%29%29
Algebra steps:
r%2B2=2r-4
0%2B2=2r-r-4
2=r-4
r-4=2
r-4%2B4=2%2B4
highlight%28r=6%29 m%2Fs, the boat in non-moving water.

Actually, the "speed through the water of the boat" in the two directions are these:
UPSTREAM, r%2B2=6%2B2=highlight%288%29 m%2Fs
DOWNSTREAM, r-2=6-2=highlight%284%29 m%2Fs