#math - Sun 1 Apr 2007 between 03:02 and 03:19

NY Lost Funds



clarity_http://rafb.net/p/PSsYTq93.html <- isn't that problem wrong
ie: the converse is true since it's an iff
http://en.wikipedia.org/wiki/Mutually_independant <- says it's an iff law
theorem rather
kmhit is correct
clarity_so the converse is not true?
kmhclarity_ : your problem does not assume mutually (pairwise)
yes
read it carefully
progekCan someone help me set up an equation? I can solve equations but have a hard time going from words to equations. It's a type of d = rt with water current.
kmhP(A_1 n .....n A_)=P(A_1).....P(A_n) is not pairwise
clarity_ : so you need to construct an small example where P(A_1 n .....n A_)=P(A_1).....P(A_n) is true but P(A_1 n A_2)=P(A_1)*P(A_2) is not
clarity_ah
progek"The current of river is 2 mph. A boat goes upstream 12 miles and returns. Total time up and down river was 5 hours. Boat speed in still water?" I understand downstream the speed (say x) is x + the current. Going upstream would be x - current and the total miles travelled are 12 * 2 right? I try setting up the equation but I fail. I was thinking something like 2.5(x+3) = 12 and 2.5(x-3 = 12 but this does not seem right.
TRWBWprogek: time=distance/speed
john_sheuTRWBW: aha, wrong!
progekah ok, so after I figure out the time I would just plug that in?
TRWBWjohn_sheu: ?
john_sheutime = distance / velocity
what if speed were going the other way?
*boom tish*
TRWBWprogek: your speeds differ. you want to do time=time_up+time_down, time_up=distance_up/speed_up time_down=distance_down/speed_down
progek: it ends up simpler than it looks
kaotrixIs there such a thing as a 3D polar coordinate system?
progekok so after I get time_up/time_down and find 'time' I just plug that into the equation?
john_sheukaotrix: spherical coordinates
or cylindrical
kaotrixalright
TRWBWjohn_sheu: you know time=5h, you know speed_up and speed_down as expressions in speed_still. you know distance_up=distance_down=12 miles
john_sheu: or you can use euler angles
john_sheu: so you plug it all together you are gonna get one equation with only one unknown, speed_still
john_sheuTRWBW: well, I didn't read the context, I was just doing my generalized velocity != speed happy dance
TRWBWoops
john_sheu: i flipped a bit in my head, meant that to go to progek
progek: that last to john_sheu was for you
my bad, a cosmic ray must have hit a neuron
progekok so it's 12 miles on way, then 12 miles another way right? So there I have my distance for both up and down stream. So lets say the speed of the boat is x.. so is it something like-> 12/(x+2) 12/(x-2) ?
TRWBWprogek: it's 5=12/(x+2)+12/(x-2)
progek: didn't have any more hints to give, so just gave the answer ;)
progek:) thanks trwbw word problems are tricky for me

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