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Discussion in 'Physics & Math' started by Pim, May 27, 2003.

  1. MacM Registered Senior Member

    Messages:
    10,104
    Coconuts

    For anyone still thinking about coconuts, the fewest coconuts on the island are 25.
     
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  3. Persol I am the great and mighty Zo. Registered Senior Member

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    5,946
    Lol... yeah, I realized that right after posting. I went back and changed it a minute before you posted

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    My basic reasoning here is that the volume is constant, so I calculated it with a hole of radius 0. As the hole grows, the sphere does too. To be any simple kind of answer, it has to be constant.
     
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  5. MacM Registered Senior Member

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    10,104
    OK

    Persol,

    Found my problem. TI-55. Boolean, gotta press = more often.
     
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  7. Janus58 Valued Senior Member

    Messages:
    2,397
    Correct.
     
  8. MacM Registered Senior Member

    Messages:
    10,104
    Right but WRONG

    Well, I screwed it up but it is really strange. I calculated Persol's first wrong answer backwards and got the right radius but running the TI-55 forwards I was getting incorrect answers for volume.. Wierd. I was looking to see if indeed the volume stayed the same but my results were saying they didn't. When actually they do.

    Good problem though Janus58.
     
  9. MacM Registered Senior Member

    Messages:
    10,104
    Chicken & Eggs

    Disregarding the obvious that a half chicken doesn't exist, etc:

    If a chicken and a half, lays and egg and a half, in a day and a half.

    How many chickens does it take to lay a dozen eggs a day?
     
  10. one_raven God is a Chinese Whisper Valued Senior Member

    Messages:
    13,433
    Re: Chicken & Eggs

    12
     
  11. MacM Registered Senior Member

    Messages:
    10,104
    Nope

    one-raven,

    Nope.

    12/1.5 = 8

    8 x 1.5 = 12 but that is in 1.5 days.
     
  12. one_raven God is a Chinese Whisper Valued Senior Member

    Messages:
    13,433
    Re: Nope

    got me!

    *tries to think of a mathematical riddle*

    hmmmmmm
     
  13. ryans Come to see me about a dog hey Registered Senior Member

    Messages:
    995
    18 chickens
     
  14. MacM Registered Senior Member

    Messages:
    10,104
    Chicken Farmer

    ryans,

    Winner.
     
  15. MacM Registered Senior Member

    Messages:
    10,104
    9's

    Question on mathematics.

    As a magician (40 years ago) I did many tricks by using a unique feature of 9's.

    Why is it that digits any multiple of 9 will add to nine?


    i.e. - 9 x 71485 = 643,365

    6
    4
    3
    3
    6
    5+
    ---
    27


    2
    7+
    ----
    9

    or 9 x 9 = 81

    8
    1+
    ----
    9


    And fractals of 9 also equal fractals of 9.


    3 x 1 = 3

    3 x 2 = 6

    3 x 3 = 9

    3 x 4 = 12 = 3

    3 x 5 = 15 = 6

    3 x 6 = 18 = 9

    3 x 7 = 21 = 3

    3 x 8 = 24 = 6

    3 x 9 = 27 = 9

    etc, etc., This 3, 6, 9 sequence continues forwver.
     
  16. everneo Re-searcher Registered Senior Member

    Messages:
    2,621
    Re: 9's

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  17. MacM Registered Senior Member

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    10,104
    Oh Yea

    everneo,

    Cake in a hat, never ending ping pong balls from a card.

    In "Cake in the Hat", I borrow a hat (deep like coyboy,etc) from the audience. My wife held it upside down and I crack an egg an put in it, pour a couple pints of milk in it, a cup of flour, etc. Stir it with my wand, heat it with a candle and wahla. I would dump out cup cakes or doughnuts.

    The hat (unless I was nervous), suffers no damage.

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    PS: You don't want to play jpoker with me either. I can shuffle a desk of card until you say OK, pass the cards around for them to be cut by observers and then deal six full houses and an Ace high spade Royal Flush. Guess who gets the flush?
     
  18. ryans Come to see me about a dog hey Registered Senior Member

    Messages:
    995
    Guess who gets kicked out of the casino....

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  19. MacM Registered Senior Member

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    10,104
    Not Exactly

    ryans,

    Not exacatly, those suckers are sharper than me. I tried some stuff in Black Jack once and was up $120.00, They gave me strange looks and the next thing I new I was holding a cup on the sidewalk selling penciles.

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    Not actually but they did empty my billfold.
     
  20. Persol I am the great and mighty Zo. Registered Senior Member

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    Re: Right but WRONG

    How did try calculating the volumes without using integrals? I don't know of any simple geometric way to do it, which is why I thought it must be constant.... riddles don't using integrals

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  21. MacM Registered Senior Member

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    10,104
    Geometry

    persol,

    Vt = 4*Pi*r^3/3

    Volume Hole = Pi * r^2 * l

    Volume of Zones of one base = 2 * Pi * h^2 * (r -h/3)

    h = r - l
     
  22. Persol I am the great and mighty Zo. Registered Senior Member

    Messages:
    5,946
    Re: Geometry

    Ahhh. That works too... I tried simplifying symbolically and got something wrong in there.
     
  23. Janus58 Valued Senior Member

    Messages:
    2,397
    Re: 9's

    This has to do with the fact that 9 is the highest digit value in decimal. The same thing happens for 7 in octal, and F in hexidecimal.

    First off, we'll show that any digit multiplied by 9 will result in a product who's digits add up to nine.

    start with A*9, with A being any single digit number.

    this is the same as A*(10-1) or A*10 - A

    since A stands for a single digit we'll write A*10 as A0 which gives us:

    A0
    -A

    Subtracting the 'ones column we have 0-A , borrowing the 'tens' column we get 10-A for our 'ones' digit of the product.

    subtracting the 'tens' column, we have (A-1 - 0) since we borrowed. earlier. giving us the product digits of (A-1) and(10-A)

    adding them gives (A-1+10-A) , the A's cancel out leaving 10-1 = 9

    two digit numbers work like this:

    AB*9

    AB*(10-1)

    AB0
    -AB

    if B>A this gives digits of (A),(B-1-A)&(10-B) added together:

    A+B-1-A+10-B : A's and B's cancel out, Leaving 10-1 =9

    B<A gives digits of (A-1),(10+(B-1)-A) & (10-B) added together:

    A-1+10+B-1+10-B A's and B's still cancel out, leaving -1+10-1+10 or (9+9)

    We've already shown that adding the digits of the sum of 9+9 or 2*9 will equal nine.

    three digits:

    ABC * 9

    ABC *(10-1)

    ABC0
    -ABC

    ..... and so on

    Its easy to see that no matter how many digits we have:

    The Individual digits(A B C's etc) cancel out

    The one's column produces a 10 which results in a -1 somewhere down the line.

    Every 10 produced by borrowing creates a -1 , meaning after you cancel out the individual digits, you are always left with at least one (10-1) pair each which reduces to a 9.

    result: the sum of the digits of any product of 9 equals 9 (in decimal)
     

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