Cadbury Mystery

Keith Hayward has sent this.

Don't tell me your age;
you probably would tell a falsehood anyway - but
the Cadbury Man will know!

This is pretty neat.

It takes less than a minute .
Work this out as you read .
This is not one of those waste of time things, it's
fun.

1. First of all, pick the number of times a week that you
would like to have chocolate (more than once but
fewer than 10)

2. Multiply this number by 2 (just to be bold)

3. Add 5

4. Multiply it by 50 -- I'll wait while you get the
calculator

5. If you have already had your birthday this year add 1759

If you haven't, add 1758.

6. 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 have chocolate each
week).

The next two numbers are

YOUR AGE! (Oh YES, it is!!!!!)

THIS IS THE ONLY YEAR (2009) IT WILL EVER WORK, SO SPREAD
IT AROUND TO YOUR FRIENDS WHILE IT LASTS

The last few posts on calculations made me think and use algebra to solve this one.
My calculations are given beow,
Let the number thought be a
Step 2.............a*2
Step 3.............(a*2 +5)
Step 4.............(a*2 +5)*50 = 100a + 250
Step 5.............(100a + 250) + 1759 = 100a + 2009
Step 6..............100a = 2009 - 1948 ...1948 is my year of birth

Now this is a three digit number.
When you subtract the year of birth from this year 2009, you naturally get your age.
100a gives you the hundreds column in the three digit number, which is the single digit number of chocolates which cadbury gave you.

You see, Algebra has many uses, besides mundane formulae like (a+b)(a+b)=.....

Once a mother was telling her friend of the new subjects being taught to her daughter in School.
"My Lucy is being taught French, German, Latin and Algebra in School", pointing proudly to her daughter.
Then as is the habit with mothers, she called out to Lucy to come.
"Come Darling, tell Mrs. John, how do you do in Algebra"