9+3

Jack: Hey Dad, What's 9+3?

Dad: What?

Jack: 12

Dad: Very good, how did you know that?

Jack: It was in my imagination.

Dad: (laughter)

Jack:  Hey Dad, What's 9+3+3?

Dad:  What?

Jack: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15.

Dad: Are you sure your only 4 years old?