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Thread: Puzzles for you

  1. #1
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    Default Puzzles for you

    solve this puzzle:

    In a country in which people only want boys, every family continues to have children until they have a boy. If they have a girl, they have another child. If they have a boy, they stop. What is the proportion of boys to girls in the country? Assume these are infinite families in the country?

    From i_online

  2. #2
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    If we consider, n as the total number of families,

    Then the ration of number of boys to girls will always be 2:n, where n is the number of family and n>=1

    Thanks

  3. #3
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    i'm sorry but i'm not very good with math(also with English)
    so is his answer were right?
    it's seems to be logical .
    any way this is a great puzzle, do you have one that not involved with math?

  4. #4
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    nice puzzle.
    Keep sharing.

  5. #5
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    Multiply of 37 by multiplies of 3:
    3 x 37 = 111
    6 x 37 = 222
    9 x 37 = 333
    12 x 37 = 444
    15 x 37 = 555
    18 x 37 = 666
    21 x 37 = 777
    24 x 37 = 888
    27 x 37 = 999


    Nice one:
    111.111.111 x 111.111.111 =
    12.345.678.987.654.321


    Trapeze:

    1 x 9 + 2 = 11
    12 x 9 + 3 = 111
    123 x 9 + 4 = 1111
    1234 x 9 + 5 = 11111
    12345 x 9 + 6 = 111111
    123456 x 9 + 7 = 1111111
    1234567 x 9 + 8 = 11111111
    12345678 x 9 + 9 = 111111111
    another Trapeze:

    1x 8 + 1 = 9
    12 x 8 + 2 = 98
    123 x 8 + 3 = 987
    1234 x 8 + 4 = 9876
    12345 x 8 + 5 = 98765
    123456 x 8 + 6 = 987654
    1234567 x 8 + 7 = 9876543
    12345678 x 8 + 8 = 98765432
    123456789 x 8 + 9 = 987654321

    and another one:

    0x 9 + 8 = 8
    9 x 9 + 7 = 88
    98 x 9 + 6 = 888
    987 x 9 + 5 = 8888
    9876 x 9 + 4 = 88888
    98765 x 9 + 3 = 888888
    987654 x 9 + 2 = 8888888
    9876543 x 9 + 1 = 88888888
    98765432 x 9 + 0 = 888888888
    987654321 x 9 - 1 = 8888888888
    9876543210 x 9 - 2 = 88888888888

  6. #6
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    Nice puzzle.
    Keep going neerajsingh.

  7. #7
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    This thread made into Sticky. If it is not updated daily it will be removed.

    @i_online, in view of making this thread sticky two of your puzzles have been added here and your original posts are moved.
    Cheers
    indianbaba.

  8. #8
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    Thanks indianbaba for making this thread sticky. It would surely help others.

    Finger Multiplication
    by Sidney Kolpas
    Mathematics Teacher April 2002


    It requires that the students hold both hands up, with palms facing the student. The student counts his or her thumbs and fingers consecutively
    from left to right, with the thumb on the left hand representing the number 1 and the thumb on the right hand representing the number 10. To multiply n times 9, where 1 <= n <= 10 and where n is a whole number, the student bends down the nth finger. The number of fingers to the left of the bent finger represents the tens-place digit of the product, whereas the number of fingers to the right of the bent finger represents the ones-place digit of the product.

    The figure below illustrates 7 x 9.





    Mr. Kolpas explains why this works in his article in the April 2002 issue of the Mathematics Teacher.
    Courtesy : http://www.pen.k12.va.us

  9. #9
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    i never knew that.
    That was something marvellous.
    Keep sharing.

  10. #10
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    Finger Multiplication by Nine
    by Paul Horrell
    Mathematics Teacher February 2003


    The "finger folding" multiplication by 9 can be expanded to include multiplicands up to 99.

    Code:
    The algorithm used is similar to the following:
    
    To multiply a two-digit number by 9, 
    ENTER the multiplicand by forming a V between the tens-digit finger and the next finger to its right (SPREAD). 
    
    ENTER the units digit by FOLDing the units-digit finger.
    Code:
    To read the product
    
    Hundreds digit: Count the standing fingers before the SPREAD.
    
    Tens digit: Moving from left to right, count the fingers from the SPREAD to the FOLD; wrap around if necessary.
    
    Units digit: Count the standing fingers to the right of the FOLD.
    Code:
    Example:
    48x9
    
    Enter (1 2 3 4 _ 5 6 7 F 9 0)
    
       Read:
       Hundreds (1 2 3 4) 4
       Tens (5 6 7) 3
       Units (9 0) 2
    
    Example with wraparound:
    83 x 9
    
    Enter (1 2 F 4 5 6 7 8 _ 9 0)
    
       Read:
       Hundreds (1245 6 78) 7
       Tens (9 0 1 2) 4
       Units (45 6 7890) 7

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