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 |

kmh | it is correct |

clarity_ | so the converse is not true? |

kmh | clarity_ : your problem does not assume mutually (pairwise) yes read 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 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. |

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 / velocity what 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_down progek: 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 coordinates or 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 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_sheu | TRWBW: well, I didn't read the context, I was just doing my generalized velocity != speed happy dance |

TRWBW | oops 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 |

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 |