If the current has a speed of 4mph find the speed of the boat in still water.
2007-02-20 05:27:52 · 3 answers · asked by kp 2 in Science & Mathematics ➔ Geography
The boat is traveling at 36 mph under its own power or on "still water". It traveled for 30 minutes (1/2 hour) in each direction.
HOW TO SOLVE:
You know the total distance that the boat "drifted" was 4 miles (the difference between the upstream and downstream distances)
20miles - 16miles = 4 miles of drift.
and the flow rate of the stream is 4 mph.
Therefore, time on the water had to be 1 hour, or 0.5 hours in each direction. Now you can solve for MPH
(X mph + 4mph) x 0.5hrs = 20 miles
X mph + 4 mph = 40 mph
X mph = 36 mph
Check your work by substituting:
Down stream. (36mph + 4 mph) 0.5 hrs = 20 miles
Up Steam (36mph - 4mph) 0.5 hours = 16 miles
So if it were on a lake or other still body of water, the boat would travel at 36 mph.
This really should have been in the algebra questions.
2007-02-20 05:57:00 · answer #1 · answered by dustoff 3 · 0⤊ 0⤋
Speed of the boat going downstream=24 Speed of the boat going upstream=16 Speed of the boat by itself=20 Speed of the current=4 You can solve this by the Distance=Rate * Time Speed going downstream: 8=1/3x (20 minutes=1/3 of an hour) Speed going upstream: 8=1/2x (30 minutes=1/2 of an hour) {You have to convert the time into fractions because since the distance was in miles, we have to express the speed in Miles per HOUR... there are 60 minutes in an hour so 20 minutes is 20/60 or 1/3 and 30 minutes is 30/60 or 1/3} Now you can set up a system of equations to find the speed of the boat and speed of the current. Let X= the speed of the boat and Y= the speed of the current. You can say the following... X+Y=24 (You know the speed of the boat going with the current is 24) X-Y=16 (You know the speed of the boat when it was going against the current was 16) You now have two equations you can solve by whatever means you've learned so far... personally I like addition because it's more intuitive and easier for me... You just put one eqation over the other and add the like terms. (In other equations you may have to multiply one of the equations so one of the variables cancels out, but since in this one we have a positive y and a negative y, they will already cancel out. So you have somthing that looks kind of like this: x+y=24 x-y=16 Adding like terms: x+x+y-y=24+16 we get 2x=40 Divide both sides by 2 and you get x=20. Since we stated that x is the speed of the boat, that is our answer. We can also find the speed of the current by subsituting our answer back into either one of the other equations: 20-y=16 or y=4 The math itself is much easier than my wordy explanation.
2016-05-23 23:02:33 · answer #2 · answered by Anonymous · 0⤊ 0⤋
If your looking for an answer of the speed of the boat in "still" water..then the answer of its speed would be Zero mph.Nice try...: )
2007-02-20 05:32:57 · answer #3 · answered by Bert R 2 · 0⤊ 2⤋