It really isn't that surprising. You feed in all the information that it needs, it's only wrapped up inside maths code.
N = NUMBER of times a week we want to go out and eat
My birthday has already been (october 31 1981)
50(2N+5) +(1757 - 1981)
=
100N +250 + 1757 - 1981
=
100N + 2007 - 1981
=
100*the first number you thought of + this year - the year you were born
if you multiply anything by 100 you'll just shove two 0s to the end of it. if you take away the year you were born from this year you get your age.
The first digit of this was your original number
(I.e., how! Many times you want to go out to restaurants in a week.)