Squigly Squigly's Brain Teasers

Question:

If 7 is transformed into 13 and 11 is changed to 21 then what does 16 become?

Answer:

31, because I multiplied the number by 2 and subtracted one.

Try another Brain Teaser:

A boy was rushed to the hospital emergency room. The ER doctor saw the boy and said, "I cannot operate on this boy. He is my son." But the doctor was not the boy's father. How could that be?