SOLUTION: Michael rows downstream on a river. He then returns to the starting point. He traveled a total distance of 16 miles, in 6.25 hours. Michael's average rowing speed in still water

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Question 955883: Michael rows downstream on a river. He then returns to the starting point. He traveled a total distance of 16 miles, in 6.25 hours. Michael's average rowing speed in still water is 4 miles/hour. Assume the speed of the river current is constant. What is the speed of the river current?
Answer by lwsshak3(11628) About Me  (Show Source):
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Michael rows downstream on a river. He then returns to the starting point. He traveled a total distance of 16 miles, in 6.25 hours. Michael's average rowing speed in still water is 4 miles/hour. Assume the speed of the river current is constant. What is the speed of the river current?
***
let c=speed of river current
4+c=speed of rowboat downstream
4-c=speed of rowboat upstream
travel time = distance /speed
one-way distance=8 mi
..
8%2F%284%2Bc%29%2B8%2F%284-c%29=6.25
lcd:(4+c)(4-c)
8(4-c)+8(4+c)=6.25(4+c)(4-c)
8(4+c)+8(4-c)=6.25(16-c^2)
32+8c+32-8c=100-6.25c^2
6.25c^2=100-64
6.25c^2=36
c^2=±√(36/6.25)
c=±6/2.5=2.4
speed of river current=2.4 mph