## #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 wrongie: the converse is true since it's an iffhttp://en.wikipedia.org/wiki/Mutually_independant <- says it's an iff lawtheorem rather kmh it is correct clarity_ so the converse is not true? kmh clarity_ : your problem does not assume mutually (pairwise)yesread it carefully progek Can 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. kmh P(A_1 n .....n A_)=P(A_1).....P(A_n) is not pairwiseclarity_ : 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. TRWBW progek: time=distance/speed john_sheu TRWBW: aha, wrong! progek ah ok, so after I figure out the time I would just plug that in? TRWBW john_sheu: ? john_sheu time = distance / velocitywhat if speed were going the other way?*boom tish* TRWBW progek: your speeds differ. you want to do time=time_up+time_down, time_up=distance_up/speed_up time_down=distance_down/speed_downprogek: it ends up simpler than it looks kaotrix Is there such a thing as a 3D polar coordinate system? progek ok so after I get time_up/time_down and find 'time' I just plug that into the equation? john_sheu kaotrix: spherical coordinatesor cylindrical kaotrix alright TRWBW john_sheu: you know time=5h, you know speed_up and speed_down as expressions in speed_still. you know distance_up=distance_down=12 milesjohn_sheu: or you can use euler anglesjohn_sheu: so you plug it all together you are gonna get one equation with only one unknown, speed_still john_sheu TRWBW: well, I didn't read the context, I was just doing my generalized velocity != speed happy dance TRWBW oopsjohn_sheu: i flipped a bit in my head, meant that to go to progekprogek: that last to john_sheu was for youmy bad, a cosmic ray must have hit a neuron progek ok 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) ? TRWBW progek: 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