I was an Engineering Manager when a subordinate engineer blindly brought this to my attention back in 2007. He was impressed that the answer, regardless of the person, ended up as 111. I sat and looked at the equation for merely a second, and caught that when you are working with only the last two digits of a given century, the 2-digit year plus your age must equal the current two-digit-year plus 100, since what you've done is basically calculate from 1900 to present by taking your birth year and your age...hence it is nothing but a simple check-sum.

e.g.: (19)65 + 46 = 2011 = (19)00 + 100 +11 = (19)00 + 111
{equation for someone born in 1965, as calculated in 2011...the number will always come out 111 unless they are more than 111 years old, or less than 12 years old...in which case, you must work with at least three digits for it to come out correctly}

After I showed him this, and heckled his 'strong math background' from a well-known Engineering university...I gave him a month of Saturday 'overtime' to refine his 'equation analysis skills'...