At the end of the year for the past several years, a viral social media post has made the rounds that blows people's minds because it knows the year you were born. It's not magic though. It's simple math.

The post has been seen in various incarnations, but this was the popular one going around at the end of 2019.

Did you do the math? Is the number you got the last two digits of the year you were born. For most people, it will be and here's why.

The math works out because of the variable of age. No matter what number you put in there, as long as you weren't born in the 1900's, the math will always work out to be the last two digits of the year you were born.

79+40=119. That's the number of years from 1900 to 2019. Subtract your age from 119 and you'll get the year you were born.

It only works well at the end of the year however, because at that point, most people will have had a birthday in the current year. The only time it will work for everyone born in the 1900's is on December 31, 2019.

At the end of 2020, you'll get the same result by adding one year to the number of beers making it 80. So for example, on December 31, 2019, I was 48. 79-48=31. Add the 40 and you get 71. I was born in 1971.

Next year I'll be 49 on December 31. This time you use 80 beers so 80-49=31. Add the 40 and it's still 71.

It all falls apart if you weren't born in the 1900s so this won't work for more and more people as the years go by. For now though, it's fun to blow your friend's minds with this trick like I did with Lori and Brittany.