There's been an email trick going round that works like this:

You might need the chocolate calculator!
* These numbers make the trick work in the year 2016.
The first digit is the number of times you like chocolate in the week.
The last two digits are your age!
7 is the number picked and if we were born in 1991, then we would be 25 years old!

First of all, pick the number of times a week that you would like to have chocolate (more than once but less than 10)
Let's assume it's 7
Multiply this number by 2
7 x 2 = 14.
Add 5
14 + 5 = 19
Multiply it by 50.
19 x 50 = 950
If you have already had your birthday this year add 1766*.
If you haven't, add 1765*

In 2017, use 1767 if you've had your birthday or 1766 if not.

In 2018, use 1768 if you've had your birthday or 1767 if not.
Let's say we've had a birthday so we add 1766 +950 to get 2716.
Now subtract the four digit year that you were born.
Let's say we were born in 1991, so 2716 - 1991 =
**725**
You should end up with a three digit number.
Yes!

First of all, when we look at the answer 725, we know the 7 is the number we chose for chocolate. The trick makes sure that this number is multiplied by 100 so that it appears in the "hundreds" place in the answer.

As for the age, all the trick does is subtract your year of birth from this year, but it does it in a disguised way. Instead of just subtracting from 2016, it first adds 250 + 1766 to get 2016 before you subtract your birth year.

Confused? Never mind, let's do it again with algebra...

Pick the number of times a week that you would like to have chocolate. | Let's call it C |

Multiply this number by 2 | 2 x C = 2C. |

Add 5 | 2C + 5 |

Multiply it by 50. | You have to make sure you multiply both bits by 50! You get 50(2C+5) = 50 x 2C + 50 x 5 = 100C + 250 |

If you have already had your birthday this year add 1766*. If you haven't, add 1765*. |
If we've had a birthday we get 100C + 250 + 1766 = 100C + 2016 If we haven't had a birthday we get
100C + 250 + 1765 = 100C + 2015. This would make the age in the final answer one year less. |

Now subtract the four digit year that you were born. | If we were born in 1991 then:
100C + 2016 - 1991 = 100C + 25 |

You should end up with a three digit number.
The first digit is the number of times you like chocolate in the week. The last two digits are your age! |
As you can see, the three digit number is made up of 100C, (which puts your chocolate digit at the front) and the last two digits are your age. |

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