SOLUTION: A boat moves 7 km upstream in the same amount of time it moves 20 km downstream. if the rate of the current is 6 km per hour, find the rate of the boat in still water.

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Question 431388: A boat moves 7 km upstream in the same amount of time it moves 20 km downstream.
if the rate of the current is 6 km per hour, find the rate of the boat in still water.
Found 2 solutions by htmentor, ewatrrr:
Answer by htmentor(1343) (Show Source):
You can put this solution on YOUR website!
Let s = the rate in still water
Let c = the rate of the current = 6 km/hr
Let t = time
So the upstream rate = s - c
And the downstream rate = s + c
Since time = distance/rate, we can write
t = 7/(s-c)
t = 20/(s+c)
Equating the RHS, and subsituting the value for c gives:
7/(s-6) = 20/(s+6)
Cross multiply:
7s+42 = 20s-120
Solving for s gives:
13s = 162 -> s = 12.462 km/hr

Answer by ewatrrr(24785) (Show Source):
You can put this solution on YOUR website!

Hi
Let x represent the rate of the boat in still water.
Question states*** Note t = D/r (times the same)
| Cross Multiplying
7(x+6) = 20(x-6)
162 = 13x
x = 12.4615kmph
CHECKING our Answer***
7/6.4615 = 20/18.4615 = 1.0833