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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- Dec 9th 2006, 09:13 AMgetmathA 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? - Dec 9th 2006, 09:26 AMTriKri
- Dec 9th 2006, 11:33 AMSoroban
Hello, getmath!

Another approach . . .

Quote:

John was born in $\displaystyle 19ab$.

The two-digit number $\displaystyle ab$ when divided by 2 gives his age on his birthday in 1999.

Can you tell me how old was he?

Let $\displaystyle x\,=\,ab$

He was born in the year $\displaystyle 1900 + x$

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

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

Therefore, he was born in $\displaystyle 1966$; he was $\displaystyle 33$ in 1999.

- Dec 9th 2006, 12:45 PMOReilly
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

$\displaystyle 1999 - \frac{{10a + b}}{2} = 1900 + 10a + b$

where $\displaystyle 10a + b$ is that ab two digit number. - Dec 9th 2006, 07:40 PMgetmath