3 Logic Puzzles

1.
A young man approached a guard outside two locked doors, one orange, the other blue.

"Greetings," said the guard. "Behind one door is a lovely princess, behind the other, a man-eating tiger. To discover which room has the princess, you must solve a series of logic puzzles, each more -- "

"Excuse me," interrupted the young man. "But I can't hear you while the tiger behind the orange door is always roaring."

2.
A middle-aged professor posed a logic puzzle to his student. The student says, "Couldn't I spend the time I'd use solving this puzzle on something more productive?"

3.
An old man encountered two guards standing outside a door.

"I only tell the truth," said the first guard.

"We only tell the truth," said the second guard.

"No, only one of us tells the truth, while the other always lies."

"I see," said the old man. "If I can point out who's lying and who's telling the truth, you'll let me go through the door?"

"No," said the first guard.

"We also don't stab old men and eat their organs," said the second guard.