SOLUTION: A sailboat can travel 60 miles upstream in the same time it takes to travel 100 miles downstream. If the speed of the boat in still water is 20 miles per hour, what is the speed of

Algebra ->  Finance -> SOLUTION: A sailboat can travel 60 miles upstream in the same time it takes to travel 100 miles downstream. If the speed of the boat in still water is 20 miles per hour, what is the speed of      Log On


   

Question 1194505: A sailboat can travel 60 miles upstream in the same time it takes to travel 100 miles downstream. If the speed of the boat in still water is 20 miles per hour, what is the speed of the current?
Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
              SPEED           TIME          DIST.

UPSTR         20-c             t              60

DOWNSTR       20+c             t             100

Value of t is equal both to 60%2F%2820-c%29 and to 100%2F%2820%2Bc%29, so meaning highlight_green%2860%2F%2820-c%29=100%2F%2820%2Bc%29%29.

Simplify and solve for c.
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Same type exercise comes up too often.
Something moves upstream for U distance in the same time as it moves D distance downstream. The craft or vehicle normally moves at R speed in absence of stream or river current.
What is the speed of the current? 
              SPEED           TIME          DIST.

UPSTR         R-c             U/(R-c)         U

DOWNSTR       R+c             D/(R+c)         D

U%2F%28R-c%29=D%2F%28R%2Bc%29

U%28R%2Bc%29=D%28R-c%29
UR%2BUc=DR-Dc
Uc%2BDc=DR-UR
%28U%2BD%29c=R%28D-U%29
highlight_green%28c=R%28%28D-U%29%2F%28D%2BU%29%29%29