Trick your principal into telling you their age by asking them the following:
1.
Add 1 to the number of the month in which you were born.
2.
Multiply by 100.
3.
Add the day of the month in which you were born.
4.
Multiply by 2.
5.
Add 11.
6.
Multiply by 5.
7.
Add 50.
8.
Multiply by 10.
9.
Add your age.
10.
Add 61.

 

Now ask for the resulting number and subtract 11,111.

From the right, the pairs of digits give the person's age, day of the month in which they were born, and birth month.

How does it work?