EPT+ Show Spoiler +
Pretty much it, wanna give the actual number though? ;P
[SFW] Riddles / Puzzles / Brain Teasers - Page 22
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NTTemplar
609 Posts
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ninjafetus
United States231 Posts
On May 07 2012 03:23 annul wrote: + Show Spoiler + this is wrong because it is NOT 1/2 to get the first orange ball. it is 1/1. 100%. the question has given it already. you do not multiply here for two events because there are not two events. there is only one event. + Show Spoiler + Yes, that's the point of conditional probability. The question is "What's the probability of the other ball in the pocket being orange?" The tree takes into account the different ways the first ball can be orange, and then sees is the second ball would also be orange. But fine, let's look at it your way. The first event already happened. The orange ball was chosen. How many ways could that happen? Three. (circled in orange on the chart). So the first event already happened, and it's one of those three positions. Good! Now, of those three, how many would lead to the second ball being orange? Two. (boxed in blue) Two out of three. 2/3. | ||
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soccerdude
United States54 Posts
In the problem does it specifically state that you draw an orange ball from the pocket? Yes! Therefore, drawing the orange ball out of the pocket has a 1/1 chance. It is given in the problem, and as I said before, will happen 100% of the time. Try solving from this point, knowing this information, and see what the answer is. | ||
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lithiumdeuteride
96 Posts
(9!)^(9!) = 6.447187947948624*10^2017526 | ||
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Mr. Wiggles
Canada5894 Posts
Riddle 1: Chocolate Bars You have a rectangular chocolate bar marked into m x n squares, and you wish to break up the bar into its constituent squares. At each step, you may pick up one piece and break it along any of its marked vertical or horizontal lines. However, you must not stack two pieces and break them together. Prove that every method finishes in the same number of steps. How many steps? + Show Spoiler [Solution] + It takes mn-1 steps to break apart the bar. Each time you break the bar, you increase the number of pieces by one. The method you use is irrelevant, since you always increase the number of pieces by one with each step, and you stop when you finish breaking up the bar. Riddle 2: Infection Nine 1x1 squares of a 10x10 board are infected. In one time unit, the cells with at least two infected neighbour cells (having a common side) become infected. Can the infection spread to the entire board? + Show Spoiler [Hint] + What "measure" of infected cells does not increase? + Show Spoiler [Solution] + No, the entire board cannot be infected. The perimeter of all infected areas on the board is invariant. The maximum perimeter achievable with an arrangement of 9 infected cells is 36, whereas the perimeter of the board itself is 40. So, the board cannot become completely infected no matter the arrangement of the starting infected cells. Riddle 3: Who wins? A row of minuses are written on a piece of paper. Two players take turns in replacing either a single minus or two adjacent minuses by pluses. The one who cannot make a move loses. Is there a winning strategy? + Show Spoiler [Hint] + Think of symmetry. + Show Spoiler [Solution] + Yes, there is a winning strategy. The player who has the first move will always win if they play optimally. The strategy is as follows: First turn either the middle minus, if the total number is odd, or the middle two minuses if the total number is even. Now the row of minuses is divided into two sections. To win, exactly copy you opponent's moves onto the opposite section from where he makes them. When he takes the final move in one section, you take the final move in the other, and he will be left with no available moves on his next turn. You win. | ||
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minitelemaster
United States95 Posts
You have 10 bottles of unmarked, visually identical pills and a scale. In 1 of the 10 bottles, the pills are lethal. A lethal pill weighs slightly more than a regular pill (1.1g opposed to 1.0g). How do you determine which bottle contains the deadly pills with only one measurement? Hint: + Show Spoiler + There are several ways to do this, some don't even require use of the scale. Think density. Answer: + Show Spoiler + Take 1 pill from bottle 1, 2 pills from bottle 2, etc., then weigh the total amount. The amount of additional weight above what the the total should be, assuming all regular pills, will tell you which bottle contains the lethal pills. | ||
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frogrubdown
1266 Posts
On May 07 2012 04:48 lithiumdeuteride wrote: In case anyone was wondering: (9!)^(9!) = 6.447187947948624*10^2017526 I'll take your word for it, but it's already been pointed out that that's not the biggest. There isn't an upper bound. | ||
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blubbdavid
Switzerland2412 Posts
I also thought that it was 50/50 for a long time, but in reality it is 2/3 god I suck with probability because: There is a 2/3 probability that the first chosen orange ball is from the bag with two orange balls | ||
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Zato-1
Chile4253 Posts
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soccerdude
United States54 Posts
On May 07 2012 05:06 blubbdavid wrote: + Show Spoiler [marbles] + I also thought that it was 50/50 for a long time, but in reality it is 2/3 god I suck with probability because: There is a 2/3 probability that the first chosen orange ball is from the bag with two orange balls + Show Spoiler + On the marbles question: Many of you have already closed your mind to the fact that the other side might be right. You have stopped reading what your counterpart might be saying, and instead post the same off-topic response countless times. + Show Spoiler + In the problem does it specifically state that you draw an orange ball from the pocket? Yes! Therefore, drawing the orange ball out of the pocket has a 1/1 chance. It is given in the problem, and as I said before, will happen 100% of the time. Try solving from this point, knowing this information, and see what the answer is. | ||
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insectoceanx
United States331 Posts
On May 07 2012 10:39 soccerdude wrote: + Show Spoiler + On the marbles question: Many of you have already closed your mind to the fact that the other side might be right. You have stopped reading what your counterpart might be saying, and instead post the same off-topic response countless times. + Show Spoiler + In the problem does it specifically state that you draw an orange ball from the pocket? Yes! Therefore, drawing the orange ball out of the pocket has a 1/1 chance. It is given in the problem, and as I said before, will happen 100% of the time. Try solving from this point, knowing this information, and see what the answer is. So we have 2 pockets A and B and each has two balls, A has 2 oragne 1 and 2 and B has white and orange 1 and 2. That means of the two possible pockets there are these outcomes. Pocket A Ball 1 = Second ball will be orange Pocket A Ball 2 = Second ball will be orange Pocket B Ball 2 = Second ball will be white 2/3 Ball will be orange 1/3 Ball will be white | ||
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frogrubdown
1266 Posts
On May 07 2012 10:39 soccerdude wrote: + Show Spoiler + On the marbles question: Many of you have already closed your mind to the fact that the other side might be right. You have stopped reading what your counterpart might be saying, and instead post the same off-topic response countless times. + Show Spoiler + In the problem does it specifically state that you draw an orange ball from the pocket? Yes! Therefore, drawing the orange ball out of the pocket has a 1/1 chance. It is given in the problem, and as I said before, will happen 100% of the time. Try solving from this point, knowing this information, and see what the answer is. I can't imagine what compelled you to copy and paste this nonsense a mere 8 posts below its original location. But what do I know? My mind has probably just been "closed" by actually understanding math and conditional probabilities. | ||
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xxpack09
United States2160 Posts
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rrdz
United States20 Posts
On May 07 2012 03:16 annul wrote: i disagree. + Show Spoiler + once you KNOW you drew an orange ball, the math changes. it does not matter which orange ball you have drawn. the question says only "you drew an orange ball." so, if you drew an orange ball in the O-O pocket, it's a 100% chance to draw another orange. if you drew an orange ball in the O-W pocket, it's a 0% chance to draw another orange. you cannot ever draw an orange ball in the W-W pocket, so this is discounted for math purposes. because you have already given the outcome of event #1, you don't multiply two events for probability. it's only one event, and in the given situation, only two outcomes: O-O or O-W pocket. 50/50. You are wrong because you are only considering 1 orange ball from the pocket that has two. Once you know you get an orange ball as you said.... There are only three possible outcomes..... 1 ) orange ball from orange-white pocket.... (which will result in the other ball being white)... 2) orange ball from orange orange pocket... which will result in orange being the other ball...... AND 3) the one you forgot............ you get the other ball from the orange orange pocket.... which results on the other ball being orange.... so as many have said 2/3 is the answer | ||
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MercilessMonkey
Canada150 Posts
On May 07 2012 14:44 xxpack09 wrote: soccerdude, you should look up the "Monty Hall Problem," and why the solution is to switch. Open your mind; you might learn something. Very true. There is only one right answer, and how you get to it will be logically demonstrated by this problem. Warning: said problem might blow your mind if you don't understand conditional probabilities. http://en.wikipedia.org/wiki/Monty_Hall_problem Link since everyone should read  Said logic and way of thinking can help with a lot of riddles | ||
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MercilessMonkey
Canada150 Posts
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soccerdude
United States54 Posts
I was wrong about the problem, and because of the complete sense of hierarchy I compelled through my word choice I definitely understand the backlash. Hopefully in the future I take a little more time reading the problem before posting some radical response. On a side note, I had already heard and understood the Monty Hall problem before I saw the marbles question, I just made a pretty big error in solving the marbles question that was unrelated to the Monty Hall problem. I also like the responses on opening my mind; they were very creative. | ||
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frogrubdown
1266 Posts
On May 08 2012 12:28 soccerdude wrote: Rather than lurk in the shadows I have decided to come out and say it: My post was idiotic and wrong. I was wrong about the problem, and because of the complete sense of hierarchy I compelled through my word choice I definitely understand the backlash. Hopefully in the future I take a little more time reading the problem before posting some radical response. On a side note, I had already heard and understood the Monty Hall problem before I saw the marbles question, I just made a pretty big error in solving the marbles question that was unrelated to the Monty Hall problem. I also like the responses on opening my mind; they were very creative. Thanks for being so mature about this (certainly more than I was). You should have a bright future here. | ||
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Chronos.
United States805 Posts
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frietjeman
Netherlands26 Posts
5+5+5=550 I don't know the answer  Saw this on a children's drawing plate and I was a bit amazed that I actually couldn't figure it out.Maybe the makers made a mistake or I'm just missing something really obvious here. | ||
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