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GrandInquisitor
New York City13113 Posts
I've long been a fan of riddling, and so far I've had 8 very favorite ones that I think are extremely difficult. This is a challenge to TL - if they can solve these (WITHOUT GOOGLING OR CHEATING)
Honestly, I think 1 & 2 & 8 are the hardest and I doubt anyone can get them.
(and yes I do know the answers to them. Most of them I solved myself, but not #2 or #6)
EDIT: ALL OF THEM HAVE BEEN SOLVED. =D
1. You have 2 pieces of string of different, unspecified length, and some matches. Each piece of string takes one hour to burn, but the burn rate is not constant. This means that it could take 59 minutes to burn the first 1/4, and 1 minute for the rest. The strings have different burn rates, and of course you don't know the rates anyway.
Using only the matches and the strings, measure 45 minutes.
2. You have a very nice, shiny watch. But this is no ordinary watch. This watch can answer two yes or no questions 100% accurately per day. You ask, and either a blue or yellow light will flash. Unfortunately, you don't know which light means yes and which light means no, and you can never find out because there's a 50-50 chance of the lights switching every night.
You happen to be on a game show. The rules are simple. There are three doors. Behind two are goats. Behind one is a shiny red car. Obviously, you want the car. You can choose any door, after asking the watch two questions.
What are the two yes/no questions you can ask so that you will have a 100% guaranteed chance of getting the car?
3. You are in a room and there are three light switches that are turned off. The light switches are connected to three light bulbs that are in a different room. You do not know which switch is connected to which light bulb. You cannot see into that room. But you are allowed to go into that room exactly once. How can you figure out which switch is connected to which light bulb?
4. A man is in a rowing boat floating on a lake, holding a brick in his hands. He throws the brick over the side of the boat. The brick sinks quickly. Does the water level in the lake go up or down? Explain.
5. In a certain matriarchal town, the women all believe in an old prophecy that says there will come a time when a stranger will visit the town and announce whether any of the men folks are cheating on their wives. The stranger will simply say yes or no, without announcing the number of men implicated or their identities. If the stranger arrives and makes his announcement, the women know that they must follow a particular rule: If on any day following the stranger’s announcement a woman deduces that her husband is not faithful to her, she must kick him out into the street at 10 A.M. the next day. This action is immediately observable by every resident in the town. It is well known that each wife is already observant enough to know whether any man (except her own husband) is cheating on his wife. However, no woman can reveal that information to any other. A cheating husband is also assumed to remain silent about his infidelity.
The time comes, and a stranger arrives. He announces that there are cheating men in the town. On the morning of the 10th day following the stranger’s arrival, some unfaithful men are kicked out into the street for the first time. How many of them are there?
6. You are given a set of scales and 12 marbles. The scales are of the old balance variety. That is, a small dish hangs from each end of a rod that is balanced in the middle. The device enables you to conclude either that the contents of the dishes weigh the same or that the dish that falls lower has heavier contents than the other.
The 12 marbles appear to be identical. In fact, 11 of them are identical, and one is of a different weight. Your task is to identify the unusual marble and discard it. You are allowed to use the scales three times if you wish, but no more.
Note that the unusual marble may be heavier or lighter than the others. You are asked to both identify it and determine whether it is heavy or light.
7. There are 100 light bulbs lined up in a row in a long room. Each bulb has its own switch and is currently switched off. The room has an entry door and an exit door. There are 100 people lined up outside the entry door. Each bulb is numbered consecutively from 1 to 100. So is each person.
Person No. 1 enters the room, switches on every bulb, and exits. Person No. 2 enters and flips the switch on every second bulb (turning off bulbs 2, 4, 6, ...). Person No. 3 enters and flips the switch on every third bulb (changing the state on bulbs 3, 6, 9, ...). This continues until all 100 people have passed through the room.
How many of the light bulbs are illuminated after the 100th person has passed through the room? More specifically, which light bulbs are still illuminated, and why?
8. You have Some Terminal Condition, which necessitates taking two pills a day: one Pill A and one Pill B. If you neglect to take either pill, you die; if you take more than one A or more than one B, you die. If you don't take them at exactly the same time, you die.
This morning you are going through your usual routine. You pick up your bottle of A Pills and gently tap one into your palm. Then you pick up your bottle of B Pills and tap it, but two pills accidentally fall into your hand. You now hold three pills (one A and two Bs), you don't know which are which, and they are completely indistinguishable from each other. The A Pills are the same color as the B Pills, they are the same shape, same size -- they are identical in every respect. Man, your doctor is a dumbass. But he's a rich dumbass, because he's charging you $10,000,000 a pill! So you dare not throw any away.
Thus, the puzzle: what can you do to ensure that you take only one A Pill and only one B Pill today, without wasting any pills (either today or in the future)?
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3. You are in a room and there are three light switches that are turned off. The light switches are connected to three light bulbs that are in a different room. You do not know which switch is connected to which light bulb. You cannot see into that room. But you are allowed to go into that room exactly once. How can you figure out which switch is connected to which light bulb?
+ Show Spoiler +You turn on one switch, wait for an hour, turn it off again. Then you turn on another switch and go into the room, the lit bulb belongs to the second switch. Then you touch the other two bulbs, the hot one belongs to the first switch 
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#6 is my favorite. LTT posted it here years ago. It took me many months to solve that. I've looked up the answers to #1 and #5 before. #7 I'm sure I've looked up before but it was too lame for me to remember or care. #4 is dumb. #3 is old.
Does #8,
+ Show Spoiler +Have anything to do with cutting the pills in half?
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8
+ Show Spoiler +
Cut each pill into half, and eat each one. So you will have eaten 1/2A, 1/2B,1/2B and left with 1/2A, 1/2B,1/2B. Take another A from bottle and eat 1/2, so total you would have eaten 1A, 1B.
With 1/2A, 1/2B, 1/2B left, next day just eat those and another 1/2A from the bottle.
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So here's the attempt to solve first riddle:
+ Show Spoiler +We burn the 1st string from TWO SIDES and second string from ONE side. After 30 minutes 1st string is down and the second will burn for the next 30 minutes. So basically after 30 minutes we have only one string left and we know that 30 minutes expired, and the second string will burn for 30 minutes. Now we burn it from the second side.of the string. It will be down after 15 minutes. We measured 15 minutes. 30+15 = 45 minutes.
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On September 19 2006 08:24 Ethenielle wrote:Show nested quote +On September 19 2006 08:05 GrandInquisitor wrote:
2. You have a very nice, shiny watch. But this is no ordinary watch. This watch can answer two yes or no questions 100% accurately per day. You ask, and either a blue or yellow light will flash. Unfortunately, you don't know which light means yes and which light means no, and you can never find out because there's a 50-50 chance of the lights switching every night.
You happen to be on a game show. The rules are simple. There are three doors. Behind two are goats. Behind one is a shiny red car. Obviously, you want the car. You can choose any door, after asking the watch two questions.
What are the two yes/no questions you can ask so that you will have a 100% guaranteed chance of getting the car? + Show Spoiler +I'm not entirely sure if it's allowed, but you could just ask "are there goats behind these two doors?", if you get a yes, then it's the third door, if you get a no you can ask "is there a goat behind this door(= one of the two doors you chose)", if no then it's the car, if yes then it's the other. If you can't ask about two doors at once, though..
+ Show Spoiler +You don't know which light means yes and which light means no.
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8. You have Some Terminal Condition, which necessitates taking two pills a day: one Pill A and one Pill B. If you neglect to take either pill, you die; if you take more than one A or more than one B, you die. If you don't take them at exactly the same time, you die.
This morning you are going through your usual routine. You pick up your bottle of A Pills and gently tap one into your palm. Then you pick up your bottle of B Pills and tap it, but two pills accidentally fall into your hand. You now hold three pills (one A and two Bs), you don't know which are which, and they are completely indistinguishable from each other. The A Pills are the same color as the B Pills, they are the same shape, same size -- they are identical in every respect. Man, your doctor is a dumbass. But he's a rich dumbass, because he's charging you $10,000,000 a pill! So you dare not throw any away.
Thus, the puzzle: what can you do to ensure that you take only one A Pill and only one B Pill today, without wasting any pills (either today or in the future)?
Not heard of this before so here's my guess:
+ Show Spoiler +
add one more A pill to what's in your hand (so it's a 50-50 mix) then grind it to powder then dissolve it in a known amount of water, shake/mix well before seperating into two containers. drink 1 cup today and the other cup tomorrow
You could also not dissolve in water it and just seperate out the well-mixed powder into 2 piles but that sounds less accurate to me, but may work if they don't dissolve.
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On September 19 2006 08:25 Olmer wrote:So here's the attempt to solve first riddle: + Show Spoiler +We burn the 1st string from TWO SIDES and second string from ONE side. After 30 minutes 1st string is down and the second will burn for the next 30 minutes. So basically after 30 minutes we have only one string left and we know that 30 minutes expired, and the second string will burn for 30 minutes. Now we burn it from the second side.of the string. It will be down after 15 minutes. We measured 15 minutes. 30+15 = 45 minutes.
that's pretty clever! i'd never have thought of it =]
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On September 19 2006 08:33 Resonate wrote:Show nested quote +On September 19 2006 08:25 Olmer wrote:So here's the attempt to solve first riddle: + Show Spoiler +We burn the 1st string from TWO SIDES and second string from ONE side. After 30 minutes 1st string is down and the second will burn for the next 30 minutes. So basically after 30 minutes we have only one string left and we know that 30 minutes expired, and the second string will burn for 30 minutes. Now we burn it from the second side.of the string. It will be down after 15 minutes. We measured 15 minutes. 30+15 = 45 minutes. that's pretty clever! i'd never have thought of it =]
And it only took him all of 10-15 minutes. I think he's a genius
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Really? Thanks - when I started to write this - I thought so, but when I ended, I thought "No way - it's too lame. There must be something that I cannot see". I thought it over, found nothing wrong...This must be it! ;P
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On September 19 2006 08:24 Ethenielle wrote:Show nested quote +On September 19 2006 08:05 GrandInquisitor wrote:
2. You have a very nice, shiny watch. But this is no ordinary watch. This watch can answer two yes or no questions 100% accurately per day. You ask, and either a blue or yellow light will flash. Unfortunately, you don't know which light means yes and which light means no, and you can never find out because there's a 50-50 chance of the lights switching every night.
You happen to be on a game show. The rules are simple. There are three doors. Behind two are goats. Behind one is a shiny red car. Obviously, you want the car. You can choose any door, after asking the watch two questions.
What are the two yes/no questions you can ask so that you will have a 100% guaranteed chance of getting the car? + Show Spoiler +I'm not entirely sure if it's allowed, but you could just ask "are there goats behind these two doors?", if you get a yes, then it's the third door, if you get a no you can ask "is there a goat behind this door(= one of the two doors you chose)", if no then it's the car, if yes then it's the other. If you can't ask about two doors at once, though..
You dont know which colour means yes and which colour means no though. So your not sure if the watch is saying yes or no when you ask your question
If you knew what colour meant yes and no you could just say "is there a car behind door 1?" "Is there a car behind door 2?"
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Korea (South)17174 Posts
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On September 19 2006 08:35 Olmer wrote:
Really? Thanks - when I started to write this - I thought so, but when I ended, I thought "No way - it's too lame. There must be something that I cannot see". I thought it over, found nothing wrong...This must be it! ;P
i dunno if it's the right answer, but it sounds pretty good to me =]
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regarding #1
+ Show Spoiler + plz pm if im right..
for number 1, could you just put a match down for every minute until you have 45.. you could count like
IIII with a cross through for the 5th minute etc etc till u have 9 groups..
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GrandInquisitor
New York City13113 Posts
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8th riddle (twsan inspired me - I wouldn't solve the riddle without his post here which, unfortunately, provides us with not-so-good solution but his IDEA is right)
+ Show Spoiler + Everyday you just eat one pill from each tube as if nothing wrong happened. After several days you have those 3 mixed pills and 1 pill in one of the tubes. Then you take 4 of them, cut etc (as twsan suggested). He just didn't mention that you need to eat all others before. He just wanted you to take "1/2 A pill from the tube" but he doesn't know thich tube contains A pills! When you have 4 pills remaining, it's obvious that you have 2 of each kind. Before - it wasn't. Of course this solution works if before the accident there was equal number of A and B pills.
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how do i add spoiler thingy? I have some for #2 
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Korea (South)17174 Posts
On September 19 2006 08:49 Olmer wrote:8th riddle (twsan inspired me - I wouldn't solve the riddle without his post here which, unfortunately, provides us with not-so-good solution but his IDEA is right) + Show Spoiler + Everyday you just eat one pill from each tube as if nothing wrong happened. After several days you have those 3 mixed pills and 1 pill in one of the tubes. Then you take 4 of them, cut etc (as twsan suggested). He just didn't mention that you need to eat all others before. He just wanted you to take "1/2 A pill from the tube" but he doesn't know thich tube contains A pills! When you have 4 pills remaining, it's obvious that you have 2 of each kind. Before - it wasn't. Of course this solution works if before the accident there was equal number of A and B pills.
Ummm..U do know which pills are in which bottle.
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EPT
