I got this puzzle from the Friend Who Forwards Everything:

YOUR AGE BY DINER & RESTAURANT MATH

First of all, pick the number of times a week that you would like to go out to eat. (more than once but less than 10)

Multiply this number by 2 (just to be bold)

Add 5

Multiply it by 50

If you have already had your birthday this year add 1756 …If you haven’t, add 1755.

Now subtract the four digit year that you were born.

You should have a three digit number

The first digit of this was your original number (i.e., how many times you want to go out to restaurants in a week.)

The next two numbers are YOUR AGE!

THIS IS THE ONLY YEAR (2006) IT WILL EVER WORK, SO SPREAD IT AROUND WHILE IT LASTS
Fun, but I am assuming it will work any year as long as you adjust the 1756 and 1755 part? What’s the math here? Why only a number from 2 through 9?

Multiplying the original number times 2 and then by 50 effectively places the original number in the hundreds place in the answer.

Adding 5 and multiplying by 50 adds 250 to the result. 250 + 1755 = 2006. Subtract the year you were born and you are left with your age.

These things always work the same, manipulating the numbers to put the “magic” answer in a certain digit, and adding/subtracting identical numbers. Nothing magic about it, just simple algebra.

Darn. I just calculated that out and was about to post the same findings (namely that both sides of the fonmula simplify to 100*x+2006-y where x is the eating out number and y is the year when you were born.) This means that there is no reason that this trick shouldn’t work with any number whether or not it’s between 2 and 9.

Yes – it will work for any X, where X is a positive integer. Where it fails is for people older than 99 years old. Of course, people in that age group have probably seen versions of this calculation many times before, so they won’t bother to do the sums.