You're walking down a path and come to two doors. One of the doors leads to a life of prosperity and happiness, and the other door leads to a life of misery and sorrow. You don't know which door is which.
In front of the door is ONE man. You know that this man either always lies, or always tells the truth, but you don't know which. The man knows which door is which.
You are allowed to ask the man ONE yes-or-no question to figure out which door to go through. To make things more difficult, the man is very self-centered, so you are only allowed to ask him a question about what he thinks or knows; your question cannot involve what any other person or object (real or hypothetical) might say.
What question should you ask to ensure you go through the good door?
You should ask: "If I asked you if the good door is on the left, would you say yes?"
Notice that this is subtly different than asking "Is the good door on the left?", in that you are asking him IF he would say yes to that question, not what his answer to the question would be. Thus you are asking a question about a question, and if it ends up being the liar you are talking to, this will cause him to lie about a lie and thus tell the truth. The four possible cases are:
The man is a truth-teller and the good door is on the left. He will say "yes".
The man is a truth-teller and the good door is on the right. He will say "no".
The man is a liar and the good door is on the left. He will say "yes" because if you asked him "Is the good door on the left?", he would lie and say "no", and so when you ask him if he would say "yes", he will lie and say "yes".
The man is a liar and the good door is on the right. Similar to the previous example, he'll say "no".
So regardless of whether the man is a truth-teller or a liar, this question will get a "yes" if the door on the left is the good door, and a "no" if it's not.
See also best riddles or new riddles.funnylogicshort
Your bike crashed into the dark forest and suddenly you saw and deadly panther and jaguar. You got just one bullet.
What is your escape strategy?
Simple, you must shoot the panther and drive off in the jaguar (car).logic
The Pope, Beyonce, Barack Obama, and Bill Gates are on the same plane. There are only 3 parachutes left for the 4 of them. Obama says: "As the President, I think I should have the right to have a parachute, because I rule millions of people in the greatest nation of all." Beyonce says: "As one of the greatest singers of all-time, I think I should deserve to be safe. I bring tears and laughter to millions of people, and I'm an important contributor to pop music." Bill Gates says: "As one of the richest successful company owners, I think I should live because I'm on top of the economics cycle, creating jobs and incomes for millions of people. I am a wealthy and intelligent man." Finally, the Pope says: "I'm an old, religious man. I lived a life that's full, I helped millions of people find their way through God, I'm ready to let go of a parachute and to face my fate." Which one of them will abandon the parachute and die?
Did I ever mention that the plane was crashing? No one's gonna die.cleanlogicshort
Mr. Smith has 4 daughters. Each of his daughters has a brother. How many children does Mr. Smith have?
He has 5 children, all of the daughters have the same 1 brother.logicmath
A train leaves from Halifax, Nova Scotia heading towards Vancouver, British Columbia at 120 km/h. Three hours later, a train leaves Vancouver heading towards Halifax at 180 km/h. Assume there's exactly 6000 kilometers between Vancouver and Halifax. When they meet, which train is closer to Halifax?
Both trains would be at the same spot when they meet therefore they are both equally close to Halifax.logic
You've been placed on a course of expensive medication in which you are to take one tablet of Sildenafil and one tablet of Citrate daily. You must be careful that you take just one of each because taking more of either can have serious side effects. Taking Sildenafil without taking Citrate, or vice versa, can also be very serious, because they must be taken together in order to be effective. In summary, you must take exactly one of the Sildenafil pills and one of the Citrate pills at one time. Therefore, you open up the Sildenafil bottle, and you tap one Sildenafil pill into your hand. You put that bottle aside and you open the Citrate bottle. You do the same, but by mistake, two Citrates fall into your hand with the Sildenafil pill. Now, here's the problem. You weren't watching your hand as the pills fell into it, so you can't tell the Sildenafil pill apart from the two Citrate pills. The pills look identical. They are both the same size, same weight (10 micrograms), same color (Blue), same shape (perfect square), same everything, and they are not marked differently in any way. What are you going to do? You cannot tell which pill is which, and they cost $300 a piece, so you cannot afford to throw them away and start over again. How do you get your daily dose of exactly one Sildenafil and exactly one Citrate without wasting any of the pills?
Carefully cut each of the three pills in half, and carefully separate them into two piles, with half of each pill in each pile. You do not know which pill is which, but you are 100% sure that each of the two piles now contains two halves of Cirate and half of Sildenafil. Now go back into the Sildenafil bottle, take out a pill, cut it in half, and add one half to each stack. Now you have two stacks, each one containing two halves of Sildenafil and two halves of Citrate. Take one stack of pills today, and save the second stack for tomorrow. logicshort
This is a newspaper headline:
Workers Strike - Want to Make Less Money!
What is going on?
The workers work at the mint and are tired of being overworked. They want to work less, which is making less money, since money is made at the mind!logic
There is a barrel with no lid and some wine in it. "This barrel of wine is more than half full," said Curly. Moe says, "No it's not. It's less than half full."
Without any measuring implements and without removing any wine from the barrel, how can they easily determine who is correct?
Tilt the barrel until the wine barely touches the lip of the barrel. If the bottom of the barrel is visible then it is less than half full. If the barrel bottom is still completely covered by the wine, then it is more than half full.logic
A man needs to send important documents to his friend across the country. He buys a suitcase to put the documents in, but he has a problem: the mail system in his country is very corrupt, and he knows that if he doesn't lock the suitcase, it will be opened by the post office and his documents will be stolen before they reach his friend.
There are lock stores across the country that sell locks with keys. The only problem is that if he locks the suitcase, he has no way to send the key to his friend so that the friend will be able to open the lock: if he doesn't send the key, then the friend can't open the lock, and if he puts the key in the suitcase, then the friend won't be able to get to the key.
The suitcase is designed so that any number of locks can be put on it, but the man figures that putting more than one lock on the suitcase will only compound the problem.
After a few days, however, he figures out how to safely send the documents. He calls his friend who he's sending the documents to and explains the plan.
What is the man's plan?
The plan is this:
1. The man will put a lock on the suitcase, keep the key, and send the suitcase to his friend.
2. The friend will then put his own lock on the suitcase as well, keep the key to that lock, and send the suitcase back to the man.
3. The man will use his key to remove his lock from the suitcase, and send it back to the friend.
4. The friend will remove his own lock from the suitcase and get to the documents.logic
You die and the devil says he'll let you go to heaven if you beat him in a game. The devil sits you down at a perfectly round table. He gives himself and you an infinite pile of quarters. He says, "OK, we'll take turns putting one quarter down, no overlapping allowed, and the quarters must rest flat on the table surface. The first guy who can't put a quarter down loses." You guys are about to start playing, and the devil says that he'll go first. However, at this point you immediately interject, and ask if you can go first instead. You make this interjection because you are very smart and can place quarters perfectly, and you know that if you go first, you can guarantee victory. Explain how you can guarantee victory.
You place a quarter right in the center of the table. After that, whenever the devil places a quarter on the table, mimic his placement on the opposite side of the table.. If he has a place to place a quarter, so will you. The devil will run out of places to put a quarter before you do. cleanlogicshortwhat am I
I am a mother and a father, but have never given birth. I'm rarely still, but I never wander. What am I?