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    namak's Avatar
    namak Posts: 2, Reputation: 1
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    #1

    Jan 21, 2009, 11:07 AM
    Sum of the digits
    The sum of the digits of a two digit numberis 12.if the new number formed by reversing the digits is greater than the original number by18,find the original number
    ISneezeFunny's Avatar
    ISneezeFunny Posts: 4,175, Reputation: 821
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    #2

    Jan 21, 2009, 11:39 AM

    Instead of making up a formula, do guess and check.

    Two digit number, when added together, makes 12.

    9 and 3, so 39 or 93
    8 and 4, so 48 or 84,

    So on and so forth.
    galactus's Avatar
    galactus Posts: 2,271, Reputation: 282
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    #3

    Jan 21, 2009, 12:44 PM
    Let a=first digit and b=second digit.

    Then, a+b=12.

    The original number can be expressed as 10a+b.

    In reverse, 10b+a

    So, we have 10b+a=10a+b+18

    So, you have two equations to solve for a and b


    ROLCAM's Avatar
    ROLCAM Posts: 1,420, Reputation: 23
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    #4

    Jan 22, 2009, 01:29 AM

    a + b = 12
    10b + a = 10a + b +18

    a + b = 12

    10b + a = 10a + b +18
    10b +a - 10a - b = 18
    9b - 9a = 18
    b - a = 2

    a + b = 12
    -a + b = 2

    eliminating the a's

    2b = 10
    b = 5

    if b = 5
    then a = 7

    the original number is 57

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