# Brain teasers **URL:** \ **Category:** random\ **Created:** [September 19, 2004, 11:30pm UTC](https://forum.kirupa.com/t/brain-teasers/64782 "2004-09-19T23:30:48Z")\ **Posts on this page:** 20\ **Page:** 4
**Author:** ![system](https://canada1.discourse-cdn.com/flex011/uploads/kirupa/original/3X/6/2/621e5c11736f46532526e61be85940af4230f3e5.png) [@system](https://forum.kirupa.com/u/system)\ **Post date:** [September 21, 2004, 6:11pm UTC](https://forum.kirupa.com/t/brain-teasers/64782/61 "2004-09-21T18:11:27Z")
> [@Syko](#): > > I insist it to be 1/2 as well! > > the 2nd and the 3rd are identical! IF you have 1 boy then the next one can be either a boy or a girl… it doesn’t matter if the boy is the “first” or the “second” one. > > ok… > If the “first” one is a boy then you’re left with variants 1 and 2 (SEE? only 2!), if the boy is the “second” one then you’re left with varianbts 3 and 1 (oh look! 2 again!) … so the answer is definitely 1/2 😜 well yeah, 2 identical combinations aren’t taken in account as a possibility, so definately 1/2… ---
**Author:** ![system](https://canada1.discourse-cdn.com/flex011/uploads/kirupa/original/3X/6/2/621e5c11736f46532526e61be85940af4230f3e5.png) [@system](https://forum.kirupa.com/u/system)\ **Post date:** [September 21, 2004, 6:33pm UTC](https://forum.kirupa.com/t/brain-teasers/64782/62 "2004-09-21T18:33:14Z")
> [@Syko](#): > > I insist it to be 1/2 as well! > > the 2nd and the 3rd are identical! IF you have 1 boy then the next one can be either a boy or a girl… it doesn’t matter if the boy is the “first” or the “second” one. > > ok… > If the “first” one is a boy then you’re left with variants 1 and 2 (SEE? only 2!), if the boy is the “second” one then you’re left with varianbts 3 and 1 (oh look! 2 again!) … so the answer is definitely 1/2 😜 I’ll admit that it’s a tricky one… But the answer is 1/3 🙂 You can turn it into a bar bet and win beers with it. Take two coins and say “I’ll flip these two coins. If one of the coins is heads, then I bet that the other is tails”. You’ll win two out of three bets. If you don’t believe me, then take two coins and a piece of paper and start flipping. The pattern should show up pretty fast. Another way of looking at it is to break it down into two flips: The first coin can be head or tails. 50/50 chance. If the first coin is heads, then the second can be heads or tails. 50/50 again. If the second is heads as well, then you lose. If it is tails, you win. If the first coin comes up tails, and the second comes up heads, then you win. If both come up tails, then the flip is discarded since there were no heads. So of the four possibilites, you win 2, lose 1 and 1 is discarded. So you win 2 out of 3 that aren’t discarded. ---
**Author:** ![system](https://canada1.discourse-cdn.com/flex011/uploads/kirupa/original/3X/6/2/621e5c11736f46532526e61be85940af4230f3e5.png) [@system](https://forum.kirupa.com/u/system)\ **Post date:** [September 21, 2004, 6:45pm UTC](https://forum.kirupa.com/t/brain-teasers/64782/63 "2004-09-21T18:45:36Z")
> [@Ilyas Premier](#): > > Nice one 🙂 Very tricky. > > Here’s one of my favorite: > I have 5 hats in my hands. 3 of them are white, 2 of them are black. In front of me are standing Senocular, Kirupa and Lostinbeta. I put one hat on each head, so that they can see the color of the other people’s hat but not their own. I ask them what the color of their hat is. > Senocular, seeing a white hat on Kirupa’s head and a white hat on Lost’s head, and noticing that neither of them can answer the question, says “I’m wearing a white hat”. Now how did he know that ? > > PS: This brain teaser assumes that Senocular is a bit more clever than his 2 contestants :love: I thought I knew this one, but I’ve seen this in another version where it’s Lostinbeta that knows he’s wearing a white hat even though he can’t see any of the others. ---
**Author:** ![system](https://canada1.discourse-cdn.com/flex011/uploads/kirupa/original/3X/6/2/621e5c11736f46532526e61be85940af4230f3e5.png) [@system](https://forum.kirupa.com/u/system)\ **Post date:** [September 21, 2004, 7:18pm UTC](https://forum.kirupa.com/t/brain-teasers/64782/64 "2004-09-21T19:18:34Z")
easy, lost notices that kirpua and senocular are wearing white hats and hesitates becase there is a better chance that his hat is black. and kirupa notices that senocular and lost are also wearing white hats and he too hesitates because of the greater chance of his hat is to be black… then senocular with his cleverness sees that kirupa and lost are both wearing white hats and are both hesitating to answer, realizes that they are uncertain about their guess. so senocular comes to the conclusion that kirupa sees two white hats and is uncertain about his guess as is lost. so the most reasonable answer would be white. ---
**Author:** ![system](https://canada1.discourse-cdn.com/flex011/uploads/kirupa/original/3X/6/2/621e5c11736f46532526e61be85940af4230f3e5.png) [@system](https://forum.kirupa.com/u/system)\ **Post date:** [September 21, 2004, 7:25pm UTC](https://forum.kirupa.com/t/brain-teasers/64782/65 "2004-09-21T19:25:51Z")
> [@\_azzy\_](#): > > nother one fer u fellas > A man is wearing black. Black shoes, socks, trousers, jumper, > gloves, and balaclava. He is walking down a black street > with all the street lamps off. A black car is coming toward him > with its lights off too, but somehow manages to stop in time. How > did the driver see the man? could have been a colgate (insert favorite brand of toothpaste here) smile :beam: ---
**Author:** ![system](https://canada1.discourse-cdn.com/flex011/uploads/kirupa/original/3X/6/2/621e5c11736f46532526e61be85940af4230f3e5.png) [@system](https://forum.kirupa.com/u/system)\ **Post date:** [September 21, 2004, 7:33pm UTC](https://forum.kirupa.com/t/brain-teasers/64782/66 "2004-09-21T19:33:56Z")
there are 18 roosters sitting ontop of 4 hens. the 4 hens manage to escape from underneath the 18 roosters. the 4 hens all run in opposite directions, north, east, south, and west. 6 roosters chase the hen that went north, 6 roosters chase the hen that went south, 4 roosters chase the hen that went east, and 2 roosters chase the hen that went west. the hen that went north jumps over a cliff and 4 roosters follow, leading to their death. the hen that went west runs underneath a lawnmower and 2 roosters followed, leading to their death. the hen that went east jumped into a pond and 3 roosters followed. they were all eaten by giant pond creaturesthe hen that travel south got lost in the forest along with 1 rooster and eventually starved to death.the remaining roosters went back to where they were sitting on the hens and got into a fight. 4 of the roosters were killed and 2 roosters ran away. did the other three roosters become friends? ---
**Author:** ![system](https://canada1.discourse-cdn.com/flex011/uploads/kirupa/original/3X/6/2/621e5c11736f46532526e61be85940af4230f3e5.png) [@system](https://forum.kirupa.com/u/system)\ **Post date:** [September 21, 2004, 8:16pm UTC](https://forum.kirupa.com/t/brain-teasers/64782/67 "2004-09-21T20:16:19Z")
Hang on hang on… aren’t there only two roosters left? I counted 8 total when the fight started. ---
**Author:** ![system](https://canada1.discourse-cdn.com/flex011/uploads/kirupa/original/3X/6/2/621e5c11736f46532526e61be85940af4230f3e5.png) [@system](https://forum.kirupa.com/u/system)\ **Post date:** [September 21, 2004, 8:21pm UTC](https://forum.kirupa.com/t/brain-teasers/64782/68 "2004-09-21T20:21:54Z")
> [@Ilyas Premier](#): > > I have 5 hats in my hands. 3 of them are white, 2 of them are black. In front of me are standing Senocular, Kirupa and Lostinbeta. I put one hat on each head, so that they can see the color of the other people’s hat but not their own. I ask them what the color of their hat is. > Senocular, seeing a white hat on Kirupa’s head and a white hat on Lost’s head, and noticing that neither of them can answer the question, says “I’m wearing a white hat”. Now how did he know that ? > > PS: This brain teaser assumes that Senocular is a bit more clever than his 2 contestants :love: If Senocular was wearing a black hat, then Kirupa and Lost would see one black and one white. Then Kirupa would know that he’s wearing a white hat because Lost is silent. Lost would say something if he could see two black hats. Since Kirupa doesn’t say anything, Sen can’t be wearing a black hat. And so he says that he’s wearing a white one. The version I know is this one: Sen, Kirupa and Lost are standing in front of me in a line, facing away from me. Sen is at the back of the line and can see Kirupa and Lost. Kirupa can see Lost. Lost can’t see either of the other two. I have 3 white and 2 black hats. I place one on each of them. There’s silence for a while and then Lost says “I’m wearing a white hat!”. And he’s correct. How did he know? (This one’s easier than Ilya’s, IMO) ---
**Author:** ![system](https://canada1.discourse-cdn.com/flex011/uploads/kirupa/original/3X/6/2/621e5c11736f46532526e61be85940af4230f3e5.png) [@system](https://forum.kirupa.com/u/system)\ **Post date:** [September 22, 2004, 12:15am UTC](https://forum.kirupa.com/t/brain-teasers/64782/69 "2004-09-22T00:15:48Z")
yeah…there are only two left… ---
**Author:** ![system](https://canada1.discourse-cdn.com/flex011/uploads/kirupa/original/3X/6/2/621e5c11736f46532526e61be85940af4230f3e5.png) [@system](https://forum.kirupa.com/u/system)\ **Post date:** [September 22, 2004, 12:39am UTC](https://forum.kirupa.com/t/brain-teasers/64782/70 "2004-09-22T00:39:28Z")
> [@Hans Kilian](#): > > I’ll admit that it’s a tricky one… But the answer is 1/3 🙂 > > You can turn it into a bar bet and win beers with it. Take two coins and say “I’ll flip these two coins. If one of the coins is heads, then I bet that the other is tails”. You’ll win two out of three bets. > > If you don’t believe me, then take two coins and a piece of paper and start flipping. The pattern should show up pretty fast. > > Another way of looking at it is to break it down into two flips: > The first coin can be head or tails. 50/50 chance. > If the first coin is heads, then the second can be heads or tails. 50/50 again. If the second is heads as well, then you lose. If it is tails, you win. > If the first coin comes up tails, and the second comes up heads, then you win. If both come up tails, then the flip is discarded since there were no heads. > > So of the four possibilites, you win 2, lose 1 and 1 is discarded. So you win 2 out of 3 that aren’t discarded. This is true, but you said what are the chances of the cards being the same color. They could be red and red, or black and black. Therefore 2/4, 1/2. ---
**Author:** ![system](https://canada1.discourse-cdn.com/flex011/uploads/kirupa/original/3X/6/2/621e5c11736f46532526e61be85940af4230f3e5.png) [@system](https://forum.kirupa.com/u/system)\ **Post date:** [September 22, 2004, 7:43am UTC](https://forum.kirupa.com/t/brain-teasers/64782/71 "2004-09-22T07:43:57Z")
> [@saint cleve](#): > > easy, lost notices that kirpua and senocular are wearing white hats and hesitates becase there is a better chance that his hat is black. and kirupa notices that senocular and lost are also wearing white hats and he too hesitates because of the greater chance of his hat is to be black… then senocular with his cleverness sees that kirupa and lost are both wearing white hats and are both hesitating to answer, realizes that they are uncertain about their guess. so senocular comes to the conclusion that kirupa sees two white hats and is uncertain about his guess as is lost. so the most reasonable answer would be white. Was gonna say the exact same thing :thumb: ---
**Author:** ![system](https://canada1.discourse-cdn.com/flex011/uploads/kirupa/original/3X/6/2/621e5c11736f46532526e61be85940af4230f3e5.png) [@system](https://forum.kirupa.com/u/system)\ **Post date:** [September 22, 2004, 9:03am UTC](https://forum.kirupa.com/t/brain-teasers/64782/72 "2004-09-22T09:03:43Z")
> [@Hans Kilian](#): > > Then Kirupa would know that he’s wearing a white hat because Lost is silent. then why does he still hesitate? :h: ---
**Author:** ![system](https://canada1.discourse-cdn.com/flex011/uploads/kirupa/original/3X/6/2/621e5c11736f46532526e61be85940af4230f3e5.png) [@system](https://forum.kirupa.com/u/system)\ **Post date:** [September 22, 2004, 1:31pm UTC](https://forum.kirupa.com/t/brain-teasers/64782/73 "2004-09-22T13:31:51Z")
Because he’s chicken! :lol: :pa: :run: ---
**Author:** ![system](https://canada1.discourse-cdn.com/flex011/uploads/kirupa/original/3X/6/2/621e5c11736f46532526e61be85940af4230f3e5.png) [@system](https://forum.kirupa.com/u/system)\ **Post date:** [September 22, 2004, 1:41pm UTC](https://forum.kirupa.com/t/brain-teasers/64782/74 "2004-09-22T13:41:43Z")
Saint Cleve’s “most reasonable answer” is of course wrong 😛 Hans is right though. And I knew the other one as well, but it’s really easier 🙂 ---
**Author:** ![system](https://canada1.discourse-cdn.com/flex011/uploads/kirupa/original/3X/6/2/621e5c11736f46532526e61be85940af4230f3e5.png) [@system](https://forum.kirupa.com/u/system)\ **Post date:** [September 22, 2004, 2:09pm UTC](https://forum.kirupa.com/t/brain-teasers/64782/75 "2004-09-22T14:09:02Z")
Riddle me this, Batman! Three guys check into a hotel. the clerk says it’s $10 each for a room. They each give him $10 and he shows them to their rooms. Later, he realizes that there was a special - three rooms for $25. So he takes 5 one dollar bills and goes up to the rooms. He realizes that he can’t divide 5 evenly by three, so he gives each guy $1 and keeps the remaining $2 for himself. So… Originally, there was $30. Each guest paid $9 3x9 = 27 The clerk kept $2 27+2=29 What happened to the other dollar? ---
**Author:** ![system](https://canada1.discourse-cdn.com/flex011/uploads/kirupa/original/3X/6/2/621e5c11736f46532526e61be85940af4230f3e5.png) [@system](https://forum.kirupa.com/u/system)\ **Post date:** [September 22, 2004, 2:43pm UTC](https://forum.kirupa.com/t/brain-teasers/64782/76 "2004-09-22T14:43:20Z")
> [@hsadan](#): > > then why does he still hesitate? :h: That’s IF sen was wearing a black hat. But he isn’t. ---
**Author:** ![system](https://canada1.discourse-cdn.com/flex011/uploads/kirupa/original/3X/6/2/621e5c11736f46532526e61be85940af4230f3e5.png) [@system](https://forum.kirupa.com/u/system)\ **Post date:** [September 22, 2004, 2:49pm UTC](https://forum.kirupa.com/t/brain-teasers/64782/77 "2004-09-22T14:49:16Z")
> [@Ilyas Premier](#): > > Riddle me this, Batman! > > Three guys check into a hotel. the clerk says it’s $10 each for a room. They each give him $10 and he shows them to their rooms. > > Later, he realizes that there was a special - three rooms for $25. So he takes 5 one dollar bills and goes up to the rooms. He realizes that he can’t divide 5 evenly by three, so he gives each guy $1 and keeps the remaining $2 for himself. > > So… > > Originally, there was $30. > > Each guest paid $9 > 3x9 = 27 > The clerk kept $2 > 27+2=29 > > What happened to the other dollar? euhm, am i that retarted that i can’t see the big deal about this or is this just that simple :h: each guest paid $10 3x10 = 30 the clerk kept $2 30+3 = 33 so everybody paid 11$ for a room… ---
**Author:** ![system](https://canada1.discourse-cdn.com/flex011/uploads/kirupa/original/3X/6/2/621e5c11736f46532526e61be85940af4230f3e5.png) [@system](https://forum.kirupa.com/u/system)\ **Post date:** [September 22, 2004, 2:49pm UTC](https://forum.kirupa.com/t/brain-teasers/64782/78 "2004-09-22T14:49:45Z")
There is no missing dollar- The room was $25, so each of the men paid $8.33 (1/3 of $25). The clerk keeps $2, so each man also paid $0.67 (1/3 of $2). So overall, each one of the men paid out $9, with $1 left over. (3 \* $9) + (3 \* $1) = $30 ---
**Author:** ![system](https://canada1.discourse-cdn.com/flex011/uploads/kirupa/original/3X/6/2/621e5c11736f46532526e61be85940af4230f3e5.png) [@system](https://forum.kirupa.com/u/system)\ **Post date:** [September 22, 2004, 2:54pm UTC](https://forum.kirupa.com/t/brain-teasers/64782/79 "2004-09-22T14:54:33Z")
Or you could look at it like this (probably easier): Each man paid $9. The clerk takes a $2 tip. (3 \* $9) - $2 = $25 So the clerk now has the $25 for the rooms. Each man now has $1 left over. The clerk still has his $2 tip. The clerk also has the $25 for the rooms. (3 \* $1) + $2 + $25 = $30 The trick is that you can’t add what one person has to what another person pays. In this case, you have to subtract. ---
**Author:** ![system](https://canada1.discourse-cdn.com/flex011/uploads/kirupa/original/3X/6/2/621e5c11736f46532526e61be85940af4230f3e5.png) [@system](https://forum.kirupa.com/u/system)\ **Post date:** [September 22, 2004, 2:55pm UTC](https://forum.kirupa.com/t/brain-teasers/64782/80 "2004-09-22T14:55:00Z")
that’s pretty obvious - there’s no missing dollar, and you can also look at it this way: each man had $3 left over, the clerk had $2 + their $25 for the room, so that totals $30, no big deal. however, what I’m wondering (and what i interprete the question as) is what’s wrong with the given working? edit: oops sorry, didn’t read your post cos I happened to be typing my post when you posted that 😛 [Previous page](https://forum.kirupa.com/t/brain-teasers/64782.md?page=3) [Next page](https://forum.kirupa.com/t/brain-teasers/64782.md?page=5)