SOLUTION: A motorboat travels 11 mph in still water. It travels 10 miles upstream and 10 miles downstream in a total of 5.5 hours. What is the speed of the current?

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Question 805452: A motorboat travels 11 mph in still water. It travels 10 miles upstream and 10 miles downstream in a total of 5.5 hours. What is the speed of the current?
Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
boat speed = 10 mph
current speed = x mph

against current = 10 - x
with current = 10 + x

Total distance = 11 miles Total Time= 5.50 hours
Time upstream + time downstream = 5.5 hours

11 /( 10 - x )+ 11 /( 10 + x )= 5.5
11 ( 10 + x )+ 11 ( 10 - x )= 5.50 ( 100 - 1 X^2 )
110 + 11 x + 110 -11 x = 550 - 5.5 X^2
220 - -550 = -5.5 X^2
-330 = -5.5 X^2
-5.5 X^2= -330
X^2 = 60
X = +/- 7.75 Ignore negative value
current speed = 7.75 mph