Find the speed of the stream.
2006-12-09 02:15:27 · 5 answers · asked by trjj 1 in Science & Mathematics ➔ Mathematics
Downstream
d = rt
d/t = rt/t
d/t = r . . .Use this formula
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3 = Time traveled downstream
84 = distance traved
12 = Time traveled upstrean
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84 / 3 = 28 mph
The answer is The boad traveled 84 miles at 28 miles per hour downstream
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Upstream
84 / 12 = 7
The answer is: The boat traveled 84 miles at 7 Miles per hour upstream.
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2006-12-09 02:35:04 · answer #1 · answered by SAMUEL D 7 · 0⤊ 0⤋
Use the formula distance = rate times time. d= rt
The rate is the rate of the boat (B) + the rate of the water (W) going downstream. Going upstream it is B - W
We have two equations;
Downstream; 84 = (B+W) *3
Upstream 84 = (B- W) * 12
84 = 3B + 3W
84 = 12B - 12W
divide the first equation by 3 and the second by 12:
28 = B + W
7 = B -W
ADD 35 = 2B, so B = 17.5 and W = 10.5
2006-12-09 02:17:36 · answer #2 · answered by teacher2006 3 · 1⤊ 0⤋
Let speed of stream = x
Let speed of boat be = y
84 miles in 3 hrs = 84/3 = 28 mph x+y = 28
84 miles in 12hrs = 84/12 = 7mph x-y = 7 ADD
2x = 35 hence x = 17.5mph = Speed of stream
y = 10.5mph
2006-12-09 02:30:52 · answer #3 · answered by Anonymous · 0⤊ 0⤋
Assume that the speed of the boat in still water is s and that the speed of the current in the stream is c. Then, from the problem,
3(s+c) = 3s + 3c = 84 and
12(s-c) = 12s - 12c = 84.
You solve them ☺
Doug
2006-12-09 02:20:54 · answer #4 · answered by doug_donaghue 7 · 0⤊ 0⤋
let x=speed of stream and y=cruise speed w/o current
84=3y + 3x
therefore y=(84-3x)/3 = 28-x
84=12y - 12x
84=12*(28-x) - 12x
7 = 28-x -12x
21 = 13x
x = 21/13 MPH or about 1.615 MPH
2006-12-09 02:59:23 · answer #5 · answered by Rich D 3 · 0⤊ 0⤋