EPTPuzzleing Question! (HARD) - Page 50
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baal
10541 Posts
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Chibi[OWNS]
United Kingdom10597 Posts
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Mora
Canada5235 Posts
Im extremely pleased with myself for getting 5/5/6 as an option. I have not taken any math passed grade 11. (i don't know if that has anything to do with the problem, as i used logic to work it out, not math). and baal, i am really not sure which side of the fence to sit on the whole boy/girl question. I understand all the other riddles so far, (including to goat/car one), but i do not understand your view of this boy/girl one. Many a person in this thread has explained why the girl/boy situation is dissimilar to the car/donkey one. I have not seen any1 refuting their explinations with logic. I have only seen people calling them stupid. As i am not sure who is right, would you care to disprove their arguement with logic? edit - im glad that after 50 pages, the very first riddle posted is the one still in debate. It makes me smile (if not cringe). | ||
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lastas
Sweden1219 Posts
On November 23 2004 00:09 Luhh wrote: Now I feel I just HAVE TO post here like everyone else because stupidity seems contagious :/ (the loudest preacher rule! No personal offence or flaming intended). The answer to the boy/girl problem is 2/3 because why? The hand has already been dealt! (the woman doesn't go upstairs, shag her husband and spit out another child. She had already given birth to the children. Those of you who thinks it's a 50/50 chance simply fail to see this.) Therefore it's EXACTLY the same thing as the monty/curtain/gameshow problem before they don't rearrange where the grand prize is located after the doors have been opened. Let's say you've tossed 9 tails in a row, the tenth time you toss there's a 50/50 chance to get the tenth right? true. BUT, it's a very little chance of actually getting 10 tails in a row from scratch right? True... Also what some people tried here with bogus mathematical gibberish and rephrasing of the problem to make it seem like a 50/50 chance in the boy/girl problem... One even added cases where a boy could have opened the door but didn't, but that wasn't even stated in the problem given, thus those cases DOESN'T EVEN EXIST! So please, THINK! Some people even tried to add genetics into the picture but it's assumed in the problem that she and her husband have a gene set that will result in a 50/50 chance for each child to be a boy or a girl... Remember, the keyphrase here is this "THE HAND HAS ALREADY BEEN DEALT!" You say its a small chance that you get 10 heads/tails in a row, but if you THINK, its just as small chance to get 10 heads in a row that it is to get heads, tails, heads, tails, heads, tails, heads, tails, heads, tails, in that specific order. So please, think again :-/ | ||
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Catyoul
France2377 Posts
On November 23 2004 00:09 Luhh wrote: So please, THINK! After you, sir :p As Teroru said, not a single one of the 2/3 supporters has even tried to prove our reasonings are false, while we disproved yours pretty clearly. And baal, while I agree with you on the curtains problem, I don't on the girl/boy one. On November 23 2004 00:09 Luhh wrote: Let's say you've tossed 9 tails in a row, the tenth time you toss there's a 50/50 chance to get the tenth right? true. BUT, it's a very little chance of actually getting 10 tails in a row from scratch right? True... And ? Continue your reasoning please. Oh wait, I'll do it for you if you don't mind. Ok let's say I flip a coin 10 times in a row. I write down the results. The hands have already been dealt, whoohoo  Now I have 2 questions :1. I show you the first 9 flips, they happen to be tails. What's the probability for the 10th one ? 2. I tell you there are at least 9 tails. What's the probability for the 10th one (edit: the one that isn't included in the 9 tails I told you) ? If you don't understand how these 2 questions are different, sorry I can't say much more. Btw, the correct answers are : 1. 50% tail 50% head 2. 1/11= ~9% tail 10/11 = ~91% head -- edit: Let's add a 3rd question, more tricky :p 3. I tell you there are at least 9 tails. Now, what's the probability of the flip number 10 (not the 10th one like in question 2) to be head or tail ? I'll let you think on that one before giving the answer  -- | ||
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Mora
Canada5235 Posts
<3 | ||
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Catyoul
France2377 Posts
<3 | ||
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MoltkeWarding
5195 Posts
On November 23 2004 10:46 Catyoul wrote: After you, sir :p As Teroru said, not a single one of the 2/3 supporters has even tried to prove our reasonings are false, while we disproved yours pretty clearly. And baal, while I agree with you on the curtains problem, I don't on the girl/boy one. And ? Continue your reasoning please. Oh wait, I'll do it for you if you don't mind. Ok let's say I flip a coin 10 times in a row. I write down the results. The hands have already been dealt, whoohoo Now I have 2 questions :1. I show you the first 9 flips, they happen to be tails. What's the probability for the 10th one ? 2. I tell you there are at least 9 tails. What's the probability for the 10th one (edit: the one that isn't included in the 9 tails I told you) ? If you don't understand how these 2 questions are different, sorry I can't say much more. Btw, the correct answers are : 1. 50% tail 50% head 2. 1/11= ~9% tail 10/11 = ~91% head -- edit: Let's add a 3rd question, more tricky :p 3. I tell you there are at least 9 tails. Now, what's the probability of the flip number 10 (not the 10th one like in question 2) to be head or tail ? I'll let you think on that one before giving the answer -- Actually the difference can be phrased even better. The difference is not only that a person is choosing, but discriminantly choosing. In the at least 9 out of 10 tails scenario, we have the person SELECTING the 9 tails with pre-acquired knowledge which cases are tails. Say that he randomly selected in the case of 9 tails and 1 heads. What are the chances that he will randomly select all 9 tails leaving the heads? Infinitisimal. In the boy/girl case its the same. In the case that one is a girl, you are selecting the case of which child answers the door, whereas in the case of two girls, you have two possible selections. If you're doing it based on the case that the girl is one of the children alone, then the other gender is completely unrelated to this event. It makes perfect sense. You can apply grade 1 math. 2 Children. 1 is known, 1 is random. 2-1 known = 1 random Going back to the heads/tails thing. We know that if we order the thing, there's 10x more potential for 9 tails 1 heads than for 10 tails BEFORE we flip. However it doesnt matter what order they come in, after 9 are known to be tails ?TTTTTTTTT T?TTTTTTTT TT?TTTTTTT TTT?TTTTTT TTTT?TTTTT TTTTT?TTTT TTTTTT?TTT TTTTTTT?TT TTTTTTTT?T TTTTTTTTT? In all ten scenarios ?=50% heads, 50% tails. This is the context in which the question was asked. Youre thinking of a different kind of question which isnt applicable to think sort of reasoning. The question that applies to your reasoning is: What are the odds that there will be 9 tails and 1 heads as opposed to 10 tails? This question is akin to: There are 9 tails. What are the odds that the 10th is a head? Edit: the last part responding to the previous claim about the coins | ||
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MiniRoman
Canada3953 Posts
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Catyoul
France2377 Posts
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ieatkids5
United States4628 Posts
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twsan
64 Posts
On November 23 2004 12:02 MiniRoman wrote: Flipping a coin will always be 50/50 odds. It doesn't amtter if you do it 100 times and 99 come up heads, it will be 50% heads and 50% tails (Unless it is rigged coin!). Did you all know that the more times you throw the coin their average will ALWAYS converge to 50%? even if you had a lucky 999 heads to 1 tail sequence, on AVERAGE as you throw more they will tend toward the 50/50 line. It turns out that you cannot go back to say a 51/49 split after a certain large number of independent tries. This seems intuitive but very hard to prove. It was called the "Law of Large Numbers" by Kolmogorov. Stochastics is probably the hardest math course i've taken and I'm never going to delve deeper in probability than I should've :-) | ||
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KarlSberg~
731 Posts
On November 23 2004 00:15 travis wrote: oh my god :-( Ah ah I was thinking exactly the same. Anyway I'm not gonna discuss it anymore. People who think it is 2/3, just read the whole thread to find out why you're wrong. On November 23 2004 01:18 baal wrote: if theres no dumb people left, i wouldnt feel superior so, dumb people i love you all <3 Read the whole thread and you will feel the same towards people who believe the answer is 2/3. | ||
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KarlSberg~
731 Posts
I don't think there is much to discuss since you can't find anything if you don't find the good answer and can't give much help with giving to much, still I can answer questions if someone has some. I liked it so I guess some people could like it too. Two trains start at the same time frome NY and LA, both going to the other city. (So obviously they will meet each other during their travel) LA->NY train goes at Speed1 NY->LA train goes at Speed2 The distance between both towns is D. A fly Starts from LA at the same time too. The fly is faster than both trains and goes at SpeedF. When the fly meets train2, it goes backwards until it meets train1, then it turns around again and so on. When the trains meet, what distance will the fly have flied? There are 2 ways to find the answer. One involves mathematical series and lots of calculus. The other only involves thinking. | ||
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twsan
64 Posts
so fly at time D/(speed1+speed2) will have flown speedf * D/ (speed1+speed2), the fly turning does not matter once you realize it's always traveling at the same speed. | ||
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KarlSberg~
731 Posts
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Catyoul
France2377 Posts
Btw, noone for my question 3 ? On November 23 2004 10:46 Catyoul wrote: edit: Let's add a 3rd question, more tricky :p 3. I tell you there are at least 9 tails. Now, what's the probability of the flip number 10 (not the 10th one like in question 2) to be head or tail ? I'll let you think on that one before giving the answer | ||
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twsan
64 Posts
Somewhere in Northern Eurasia, a group of 20 lemmings is planning a special group suicide this year. Each of the lemmings will be placed in a random position along a thin, 100 meter long plank of wood which is floating in the sea. Each lemming is equally likely to be facing either end of the plank. At time t=0, all the lemmings walk forward at a slow speed of 1 meter per minute. If a lemming bumps into another lemming, the two both reverse directions. If a lemming falls off the plank, he drowns. What is the longest time that must elapse till all the lemmings have drowned? | ||
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KarlSberg~
731 Posts
On November 23 2004 13:56 Catyoul wrote: Beat me to it Btw, noone for my question 3 ? In case someone wants some more time to think ****************SPOILER********************* 1/11 right? | ||
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Luhh
Sweden2974 Posts
On November 23 2004 04:21 lastas wrote: You say its a small chance that you get 10 heads/tails in a row, but if you THINK, its just as small chance to get 10 heads in a row that it is to get heads, tails, heads, tails, heads, tails, heads, tails, heads, tails, in that specific order. So please, think again :-/ Uhm sorry but you just don't get it do you? You say the same thing I said but fail to understand what I meant. Good for you... What I wrote was 1) to get a specific result in a chain from scratch with each toss at 50/50 for either outcome, the chance gets really slim to get all the exakt results in that exact order! 2) When you flip a coin it doesn't matter how many heads or tails you got in a row previously, the chance for either one is still 50/50. 3) What I meant with the hand has already been dealt is that the flips for boy/girl had already been done before the door opened, and this is what some people here doesn't grasp. She doesn't go upstairs flip for a new baby after the door has been opened, then and only then the chance would have been 50/50. now it's 2/3 since the flipping was done prior to opening the door. Geez some people... I wonder what would happen if breathing wasn't a reflex but required active thought... | ||
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