Another version of
General MacArthur's
Favorite Number Game
Take your age:
Double it:
Add 5:
Multiply by 50:
Subtract 365:
Add the loose change in your pocket:
Add 115:
The first two digits in your answer are your age,
and the last two digits are the change in your pocket.
Why don't you use some algebra to prove it?
Let a = age and c = change in your pocket.
Then following the instructions above:
Your age: a
Double it: 2a
Add 5: 2a + 5
Multiply by 50: 100a + 250
Subtract 365: 100a - 115
Add the loose change in your pocket:
100a - 115 + c
Add 115 to get: 100a + c.
(The 100 just moves the month over 2 places)