Every
year, mass emails go out challenging people to calculate their age using “Chocolate
Math”. In a minute, I’ll deconstruct the
2013 version of this fun math activity – but first, try out this (simpler)
activity:

I’m
going to read your mind, with the help of a little mathematical trickery.

1. Think
of a number – any number will work, but it’s easiest if you choose a smaller number
(between 1 and 10).

2. Add
7.

3. Take
the result and add your original number.

4. Take
the result and add 9.

5. Take
the result and divide it by 2.

6. Take
the result and subtract your

*original*number.
The number you are now thinking of is… … …

**8.**
This
result always holds (assuming you do the math correctly), regardless of your
choice of starting number.

Do
you know why? (If not, don’t worry. I’ll give the explanation a little later.)

Now,
let’s take a look at Calculating your Age by using Chocolate Math – 2013 Version.

Follow
these steps to use chocolate math to calculate your age:

1. Pick
the number of times a week that you would like to have chocolate. (More than once, but less than 10 times.)

2. Multiply
this number by 2

3. Add
5

4. Multiply
the result by 50 (followed by some joke about getting a calculator)

5. If
you have already had your birthday this year, add 1763. If not, add 1762.

6. Subtract
the four-digit year that you were born.

You now have 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 equal… YOUR AGE!

To
discover why this works (and why this version will only work in the year 2013),
we’ll need to make use of some basic Algebra skills.

Every
step of this activity is dictated to you, EXCEPT the first step… there is no
way to know how many times you will decide you want chocolate each week.

So
– let’s define a variable. Let

*x*represent the number of times you want chocolate each week.
By
writing algebraic expressions for each of the following steps, we can discover
what is happening.

Pick
a number:

*x*
Multiply
by 2 2

*x*
Add
5 2

*x*+ 5
Multiply
by 50 50(2

*x*+ 5) = 100*x*+ 250
At
this point, you have a choice based on whether or not you’ve had your birthday
this year.

If
yes, add 1763 100

*x*+ 250 + 1763 = 100*x*+ 2013
If
no, add 1762 100

*x*+ 250 + 1762 = 100*x*+ 2012
The
expression now contains 100

*x*plus the last year you had a birthday.
By
subtracting your birth year, you will end up with 100

*x*+ your age. Therefore, the first digit of your three-digit number will be the number of times you want chocolate each week, and the last two digits will be your age.
(By
the way, this activity doesn’t work for people who are more than 99 years old…
how discriminatory!!!)

Here’s
an interesting thought – there are many ways to force an algebraic expression
of either 100

*x*+ 2013 or 100*x*+ 2012. This means that, if you were so inclined, you could make up your own set of steps that would calculate someone’s age using Chocolate Math.
Now
– if you understand the math behind the Chocolate Math activity, you can
probably follow the steps in the initial activity to discover why those steps
will

*always*yield a result of**8**. If you don’t want to work through the process on your own, here it is:**.**

**.**

**.**

**.**

**.**

**.**

**.**

Think
of a number

*x*
Add
7

*x*+ 7
Add
your original number

*x*+ 7 +*x*= 2*x*+ 7
Add
9 2

*x*+ 7 + 9 = 2*x*+ 16
Divide
by 2 (2

*x*+ 16) ÷ 2 =*x*+ 8
Subtract
your original number

*x*+ 8 –*x*=**8**
With
some basic algebra skills, you too can read minds!

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For math tutorials and Silly Math Songs, visit: www.onlinemathpro.com

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