SOLUTION: A fisherman on the river rows 9 miles downstream in the same amount of time he rows 3 miles upstream. if the current is 6 miles per hour. find how lonbg it takes him to cover the

Question 157872This question is from textbook
: A fisherman on the river rows 9 miles downstream in the same amount of time he rows 3 miles upstream. if the current is 6 miles per hour. find how lonbg it takes him to cover the 12 miles. This question is from textbook

Answer by nerdybill(7384) (Show Source): You can put this solution on YOUR website!
A fisherman on the river rows 9 miles downstream in the same amount of time he rows 3 miles upstream. if the current is 6 miles per hour. find how lonbg it takes him to cover the 12 miles.
.
Apply the distance formula:
d = rt
where
d is distance
r is rate or speed
t is time
.
solving for t we get:
t = d/r
.
Let f = speed of boat in still water
.
9/(f+6) = 3/(f-6)
cross multiplying we get:
3(f+6) = 9(f-6)
3f + 18 = 9f - 54
18 = 6f - 54
72 = 6f
12 mph = f (speed of boat in still water)
.
Time traveling downstream:
t = 9/(f+6)
t = 9/(12+6)
t = 9/18
t = 1/2 hour
.
Time traveling upstream:
t = 3/(f-6)
t = 3/(12-6)
t = 3/18
t = 1/6
.
Total time:
1/2 + 1/6 = 3/6 + 1/6 = 4/6 = 2/3 hours
or, in terms of minutes
2/3 * 60 = 2 * 20 = 40 minutes

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