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Math Help - A puzzle

  1. #1
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    A puzzle

    John was born in 19ab. The two digit number ab when divided by 2 gives his age on his birthday in 1999.



    Can you tell me how old was he?
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  2. #2
    Senior Member TriKri's Avatar
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    Quote Originally Posted by getmath View Post
    John was born in 19ab. The two digit number ab when divided by 2 gives his age on his birthday in 1999.



    Can you tell me how old was he?
    1999 - age = 1900 + ab
    age = ab/2

    1999 - ab/2 = 1900 + ab
    99 = 1.5 ab
    ab = 66
    age = 33
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  3. #3
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    Hello, getmath!

    Another approach . . .


    John was born in 19ab.
    The two-digit number ab when divided by 2 gives his age on his birthday in 1999.

    Can you tell me how old was he?

    Let x\,=\,ab

    He was born in the year 1900 + x

    \frac{x}{2} years later, it is 1999.

    Hence: . (1900 + x) + \frac{x}{2} \:=\:1999\quad\Rightarrow\quad x\:=\:66

    Therefore, he was born in 1966; he was 33 in 1999.

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  4. #4
    Senior Member OReilly's Avatar
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    Quote Originally Posted by TriKri View Post
    1999 - age = 1900 + ab
    age = ab/2

    1999 - ab/2 = 1900 + ab
    99 = 1.5 ab
    ab = 66
    age = 33
    Use of symbol "ab" here is not good because it can represent a*b.

    You could've use x=ab as Soroban did.

    Beside that, everything is ok.

    I used formula
    1999 - \frac{{10a + b}}{2} = 1900 + 10a + b
    where 10a + b is that ab two digit number.
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  5. #5
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    Quote Originally Posted by OReilly View Post
    Use of symbol "ab" here is not good because it can represent a*b.

    You could've use x=ab as Soroban did.

    Beside that, everything is ok.

    I used formula
    1999 - \frac{{10a + b}}{2} = 1900 + 10a + b
    where 10a + b is that ab two digit number.
    Mathematically you are correct.
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