Which is Odd One Out and why?

4377

3954

9862

8454

9831

If,
29 - 1 = 30
9 - 1 = 10
14 - 1 = 15

Based on similar logic, Can you prove that the below algebraic equation is true?
11 - 1 = 10 ?

You walk into an old horror house. It has no power or plumbing. Once inside, you see three doors. Each door has a number on it. Behind each door is a way for you to die. Behind door number one, you die by getting eaten by a lion. Behind door number two, you die by getting murdered. Behind door number three, you die by an electric chair. You can’t turn back, so you have to go through a door. Which door do you go through?

John killed hundreds of people mercilessly and yet the police were not able to put her behind the bars. Why?

Double it and multiply it by 4. Then divide it by 8 and you’ll have it once more. What number is it?

Can you count the number of triangles in the picture below?

The more it dries, the wetter it becomes. Can you tell what it is?

If eleven plus two equals one, what does nine plus five equal?

How can you make number one disappear by adding something to it?

A thief is convicted in Mexico. He gets the death penalty. The judge allows him to say the last sentence to determine how the penalty will be carried out. If the thief lies, he will be hanged, if he speaks the truth he will be beheaded. The thief tells the last sentence and to everybody's surprise some minutes later he is set free because the judge cannot determine his penalty. What did the thief say?