How old is your teacher?

Ask your teacher (or somebody else) to

1.  Write down your house number.

2.  Double it.

3.  Add the number of days in a week.

4.  Multiply by 50.

5. Add your age.

6. Subtract the number of days in a year. (not a leap year)

7. Add 15

The answer is your teachers house number and their age!

Can you explain why this works?