Shrewdie
A very angry math teacher entered class:
"Ivan, name me a two-digit number."
"56."
"Why not 65?! Sit down, you have a D-. Peter, name me a two-digit number."
"18."
"Why not 81? D- for you, too. Abram, name me a two-digit number."
"33."
"Why not.... Abram! Stop these Jewish tricks at once!"