Question 116318
A sailboat travels 20 miles downstream in three hours. It returns in four hours. Find the speed of the sailboat in still water and the rate of the current. 
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Downstream DATA:
Distance = 20 miles ; time = 3 hrs ; rate = 20/3 mph
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Upstream DATA:
Distance = 20 miles ; time = 4 hrs ; rate = 20/4 = 5 mph
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Let the speed of the boat be "b" ; Let the speed of the current be "c"
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EQUATIONS:
b+c = 20/3 mph
b-c = 5 mph
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2b = 20/3 + 15/3 = 35/3
b = 35/6 = 5 5/6 mph (speed of the boat in still water)
Substitute to solve for "c":
35/6 + c = 20/3
c = 40/6-35/6
c = 5/6 mph (speed of the current)
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Cheers,
Stan H.