Saturday, January 8, 2011

Do You Often Ponder?

Can a man drown in the fountain of eternal life?

Paradoxical statements always have intrigued me. So have brain teasers. This post is full of points to ponder, brain teasers, and sophisms that are sure to drive anyone mad.

Have fun!..

Nobody eats at that restaurant; it's too crowded.

Answer truthfully this yes or no question: Will the next word you say be 'no'?

A crocodile living in the Nile took a child. His mother begged to have him back. The crocodile could not only talk, but was also a great sophist and stated, "If you guess correctly what I will do with him, I will return him. However, if you don't predict his fate correctly, I'll eat him." What statement should the mother make to save her child?

Your last good ping-pong ball fell down into a narrow metal pipe imbedded in concrete one foot deep.
How can you get it out undamaged, if all the tools you have are your tennis paddle, your shoe-laces, and your plastic water bottle which does not fit into the pipe?

Three men rent a hotel room for 30 dollars. They split it 3 ways and pay 10 dollars each. The hotel clerk latter decides to give them a discount of 5 dollars, so he gives 5 dollars to the bell hop and tells him to give it back to the men. The bell hop thinks to himself that he can't split 5 dollars evenly three ways so he gives each man only one dollar back and keeps two dollars for himself. Now the men have only paid 9 dollars each for the room. 9x3 is 27 dollars plus the two dollars the bell hop kept totals 29 dollars. What happened to the last dollar?

You have a pile of 24 coins. Twenty-three of these coins have the same weight, and one is heavier. Your task is to determine which coin is heavier and do so in the minimum number of weighings. You are given a beam balance (scale), which will compare the weight of any two sets of coins out of the total set of 24 coins. How many weighings are required to identify the heavier coin?

U2 has a concert that starts in just 17 minutes and all of the band members must all cross a bridge to get there. The four men begin on the same side of the bridge and you must help them to get across to the other side.
Due the age of the bridge, a maximum of two people can cross at one time. To make matters worse, it is night-time and there is only one torch. The torch is always required when crossing the bridge and the torch must be walked back and forth, it cannot be thrown, etc. Each band member walks at a different speed and a pair must walk together at the rate of the slower man:
     Bono takes 1 minute to cross 
     Edge takes 2 minutes to cross 
     Adam takes 5 minutes to cross 
     Larry takes 10 minutes to cross
For example, if Bono and Larry walk across first, it takes them 10 minutes to cross. If Bono then returns with the torch, a total of 11 minutes will have passed. There is no trick behind this, it is the simple movement of resources in the appropriate order.

Feel free to write a comment for the answer if you can't figure any of these out.  I will respond.


  1. its sad that noone actually tried to solve these riddles :(

    Mr.g you are doing such a great job for this blog
    im a big fan xD

  2. For the ping pong one, I suggest that that person buy a new pack of ping pong balls.

    For the alligator one she must answer yes and that doesn't even assure that she will get her child back in the first place, but if she answers no, it arises a paradox. The alligator cant return it because she didnt answer correctly, so then he will eat it which will affirm her answer and he should return it but not only is the child dead, but if he were to return it then her answer would be false again.

    For the hotel on since the person was taking off 5 dollars you have to stay in that same mind set. so 5 dollars off equals 25 which is the total amount of money owed. the people only got a dollar each so that brings the total to 27 and then you try to add it back to 30, but you have to stay in the same mind set of deducting the money down to 25 which is the target number. So then the guy kept 2 dollars which brings 27 down to 25 which is what the target number is.

    Now for the weigh one, im not sure what the rules are but my guess would be 5 for the minimum and 6 for the maximum. It said 2 sets of coins, so depending on interpretation whenever you get down to the 3 that weigh more than the other 3 you would have to weigh those, which would be impossible since its odd. But if you could set one aside then it would be 5 to 6. but if you cant then its impossible to find out. Or if the scale works so that you can determine which one is the heaviest since its not dropping as far the minimum would be 5 and the max would be 7.

    I am currently working on the first and last.

  3. ok so for the concert you do this
    Brono(1) takes Edge(2) over which equals 2 minutes.
    Then Brono(1) comes back to other side which eaquals 1 minutes. (he has torch)
    Then Brono hands the torch to adam.
    Adam(5) then takes larry(10) over which takes 10 minutes. (larry is SLOW!)
    adam then hands the torch to edge.
    edge(2)comes back to other side which equals 2 minutes.
    Then edge(2) and brono(1) cross which takes 2 minutes.
    When you add it all up it takes 17 minutes!

  4. for the ping pong one, it is a little too vague, but I will still attempt. What i would do is smash the bottle so it will fit (and take off cap) and tie the shoe laces firmly around the bottom of the bottle. After that I would insert the bottle into the hole and use the paddle to jam down. Hopefully the ball will fit into the cap area of the water bottle pretty snug and I will pull the water bottle out. If that doesn't work then I guess I should go get new set of ping pong balls.

  5. Well,
    - U2 = correct!
    - Alligator = catch 22 no matter what she does! It is seemingly impossible to answer this one!
    - ping pong ball = think about the properties of the ball, and assume the water bottle is full.
    - coins = It can be done in three weighings.


    Weighing 1: Break the coins into three piles of eight. Weigh one group of eight against another group of eight. If the scale balances, then the group that hasn't been weighed has the heavier coin. If the scale tips, then that group contains the heavier coin.
    Weighing 2: Break the group of eight that has the heavier coin into three groups (three coins, three coins, and two coins). Weigh one set of three against the other set of three. If it balances, the group of two has the heavier coin. If the scale tips, then that group has the heavier coin.
    Weighing 3: If the heavier coin is in the group of two, then just weigh one coin against the other to determine the heaviest coin. If the heavier coin is in a group of three, then take two of those coins and weigh them against each other. If the scale balances, the coin that hasn't been weighed is the heavier coin. If the scale tips, then that is the heavier coin.

  6. I admit defeat to the ping pong ball one and the weighing one. (Pouring the water into the pipe is genius)
    On the alligator one I thought It might be yes because I was thinking about another paradox thats stated a little differently.