maths project

You can calculate one's age by the following formula:
A = current_year - birth_year (if birthday already passed on current year)

Then, you can make up any three digit number with the age (A) as the second and third digit.

The value of this number is: R = 100n + A (where n = 1,2,3,4,5,6,7,8,9)

The trick is: you make up a maths series starting from 350 with increment of 100 (ie. 350, 450, 550, 650, 750, ...)
The general term of this series = 250 + 100n
T(n) = 50 * (5 + 2n)

Then you make up a Magic number (M) as follows:
M = current_year - 250 (for the case of birthday already passed)

Now, we can calculate the result according to the instruction as mentioned.
Resulted number = T(n) + M - birth_year (where n = 1 to 9)
= 250 + 100n + current_year - 250 - birth_year
= 100n + (current_year - birth_year)
= 100n + A
= R (which is the 3 digit number we make up above)


If current year is 2012, M = 2012 - 250 = 1762.
Use M - 1 (=1761) for the case of birthday not yet passed

how to count 250

2012-04-13 20:48:31 補充：
how to count 250