The speed of a stream is 3 mph. A boat travels 3 miles upstream in the same time it takes to travel 9 miles downstream. What is the speed of the boat in still water?
2007-09-04 14:30:28 · 6 answers · asked by DeliaS 1 in Science & Mathematics ➔ Mathematics
Suppose t is the amount of time taken (in hours), and v the speed of the boat in still water (in mph). Going upstream the speed is (v-3) mph, and going downstream it is (v+3) mph. So we have
t (v-3) = 3 <=> tv - 3t = 3
t (v+3) = 9 <=> tv + 3t = 9
Subtracting gives 6t = 6, so t = 1.
Hence v -3 = 3 and v + 3 = 9, i.e. v = 6 mph. So the boat travels at 6 mph in still water.
2007-09-04 14:33:58 · answer #1 · answered by Scarlet Manuka 7 · 0⤊ 0⤋
6 MPH. Assume the time is one hour. The current is 3 MPH working against the 6 MPH boat speed, resulting in a movement of 3 MPH. Going downstream, the 6 MPH boat movement combined with the 3 MPH current results in 9 MPH.
2007-09-04 21:34:43 · answer #2 · answered by Matt 2 · 0⤊ 0⤋
6 mile per hour...going upstream you take away the 3mph the stream is rolling and in 1 hour you travel 3 miles.....going down stream add the 3mph and you go 9 miles in an hour
2007-09-04 21:39:03 · answer #3 · answered by MICHAEL M 2 · 0⤊ 0⤋
6 mph
2007-09-04 21:35:12 · answer #4 · answered by hallock36 3 · 0⤊ 0⤋
Let's see if I understand this...
You're taking a quiz online...
If I give you the answer, you'll take credit for it. You'll also make your instructor think you have a better grip on the subject matter than you actually do. And some of those in your class will do the work themselves and get it right... or wrong... honestly. That would make them a little upset with you... and with me if they knew I gave you the answer...
The posted goal of Yahoo Answers is to help people.
So, please tell me what good my giving you the answer... or even telling you how to do the problem does you.
2007-09-04 21:39:32 · answer #5 · answered by gugliamo00 7 · 0⤊ 0⤋
6 miles in still water.
2007-09-04 21:35:51 · answer #6 · answered by TTU fan 2 · 0⤊ 0⤋