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Here is one of those math tricks that has been floating around the Internet.  Don’t cheat by scrolling down!  It takes less than a minute.  At the end, I will provide an explanation of how this trick is done.

Follow these instructions, and I will guess your age by chocolate:

	Step 1:  Pick the number of times a week that you like to eat chocolate (more than once but less than 10).
	Step 2:  Multiply this number by 2 (just to be bold)!
	Step 3:  Add 5 to the total.
	Step 4:  Multiply your total by 50 — I’ll wait while you get a calculator.
	Step 5:  If you have already had your birthday this year, add 1759.  If you haven’t, then add 1758.
	Step 6:  Now subtract the four digit year that you were born.
	Your result should be a three digit number. The first digit is your original number (i.e., how many times you want to have chocolate each week).  The next two numbers are your age!

This is the only year (2009) that this trick will work, so spread it around!

How to Solve this Trick

This is a simple algebra math trick.  For test purposes, let’s assume you were born on January 1, 1970.  That would make your age 39 (as of today, July 9, 2009).  So, following the steps above:

1. Pick the number of times a week that you like to eat chocolate.  So let’s assign the variable “C” for chocolate:
   = C
    
2. Multiply this number by 2.  So that’s:
   = C x 2 
    
3. Add 5 to the total.
   = (C x 2) + 5 
    
4. Multiply your total by 50.
   = ((C x 2) + 5) x 50
   = (C x 2 x 50) + (5 x 50)
   = (C x 100) + 250
    
5. If you have already had your birthday this year (which we have, using our test birthday of January 1), add 1759.
   = ((C x 100) + 250) + 1759
   = (C x 100) + 2009 (which is the current year!)
    
6. Subtract the four year digit you were born.
   = (C x 100) + 2009 – 1970
   = (C x 100) + 39 (which is our test age!)
   = C39

The final result is a three digit number.  The first digit is your original number “C” (C x 100).  The next two numbers are your age (39).

So the trick is to take your original number and multiply it by 100 so that it’s the first digit in the result.  Next, it multiplies and adds some numbers that equal the current year.  So then if you subtract the year you were born, the result is the number of years you have been alive, i.e., your age.

SOLVED!

If you enjoyed this puzzle, be sure to check out the Regifting Robin Mind Trick.

Article published on July 9, 2009

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