assume the number you have choose is A, then A is an integer between 1 and 7. Assume you have celebrated your birthday of this year, then put 1753 in the calculation. If you have not, then it can be shown in a similar way. Assume you were born in year B.
According to procedure, (2A+5)*50+1753-B is the final answer, which is 100A+2003-B indeed. Make sure you were born after 1903, otherwise it would be bug for this algorithm. And this will guarantee 2003-B would be the number the last two digits represent. Therefore, A is the first digit, which represents the number you choose, and 2003-B is your age.
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