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Find Missing Number

This is a discussion on Find Missing Number within the Brainteasers forums, part of the Brain Quiz category; Fill in the missing number in the series. 3,10,7,8,--,12,9,16....

  1. #1
    Junior Member
    Join Date
    Aug 2008
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    1

    Find Missing Number

    Fill in the missing number in the series.
    3,10,7,8,--,12,9,16.


  2. #2
    Expert Member
    Join Date
    Jun 2007
    Answers
    260

    Re: Find Missing Number

    hi,

    the missing number is 7.



    Sol 1.

    3 10 7 8 -- 12 9 16

    so, lets name them as

    a=3, b=10, c=7, d=8, e=?, f=12, g=9, h= 16

    a+9 gives you f(12), and b-1 gives you g(9), adn c+9 gives you h(16), so in that fashion d-1, should give you e, which will be 7 as the value of d=8.

    Thanks
    Sushma


  3. #3
    Junior Member
    Join Date
    Oct 2008
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    9

    Re: Find Missing Number

    3, 10, 7, 8
    3*2, 10+2, 7+2, 8*2
    6, 12, 9, 16
    So the missing number is 6


  4. #4
    Junior Member
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    Jan 2009
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    3

    Re: Find Missing Number

    Quote Originally Posted by TheSeeker View Post
    Fill in the missing number in the series.
    3,10,7,8,--,12,9,16.

    The missing number is 5

    Here is how i found out

    There are two sequences interwined

    one is a sequence of even numbers and another one is a sequence of odd numbers

    Consider the odd numbers and take three numbers at a time
    the lowest number is 3 and the first set of 3 odd numbers would be 3,5 and 7.
    Write them in the order of 1st, third and second ie (o1,o3,o2) this will give 3,7 and 5.
    Next set would be 9,13 and 11 and so on and so forth

    Now consider the even number. each set has three numbers in the increasing order
    The lowest numbers so far here is 8. Suppose the first set consists of (a1,a2,a3) then rewrite them by (a2,a1,a3). So a set (8,10,12) will become (10,8,12) followed by (16,14,18) and so on and so forth.

    Now combine these two sequences odd one first and in between any two odd numbers insert the even numbers and the series would unravel

    3,10,7,8,5,12,9,16,13,14,11,18,15,22,19,20,17,24....


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