math
posted by opg on .
1. First of all, pick the number of times a week that you eat chocolate. This number
must be more than one but less than ten.
2. Multiply this number by 2 (just to be bold).
3. Add 5 (for Sunday).
4. Multiply it by 50.
5. Add 1750.
6. Add the last two digits from the year you last had a birthday. So if your last
birthday was in 2009, add 9, if the your last birthday was in 2011 then add 11.
7. Now subtract the four digit year that you were born (if you remember).
You should now have a three digit number. The first digit will be your original number
(i.e. how many times you eat chocolate each week). The next two digits give your age.
Can you explain why it works?

n
2n
2n+5
50(2n+5)
50(2n+5)+1750
50(2n+5)+1750+(b%100)
50(2n+5)+1750+(b%100)b
or,
100n+250+1750b+b%100
n is shifted 2 places to the left (100n)
250+1750=2000
2000b is the last 2 digits of birth year (as long as you were born after 2000!)
If you were born before 2000, this does not work.