What always comes into a house through the keyhole?

What three numbers, none of which is zero, give the same result whether they’re added or multiplied?

If you remove one from eleven, it becomes ten. If you remove one from nine, it becomes ten.

How is this possible?

What part of the chicken has the most feathers?

What is the word or phrase below?
R | E | A | D

The product of three consecutive numbers is 7980.
Then the sum of these consecutive numbers would be?

I am lying and I always lie. Tell me whether I am lying or telling the truth.

Assume there are approximately 5,000,000,000 (5 billion) people on Earth. What would you estimate to be the result, if you multiply together the number of fingers on every person's left hand? (For the purposes of this exercise, thumbs count as fingers, for five fingers per hand.) If you cannot estimate the number then try to guess how long the number would be.

Using the clues below, what four numbers am I thinking of?

The sum of all the numbers is 31.
One number is odd.
The highest number minus the lowest number is 7.
If you subtract the middle two numbers, it equals two.
There are no duplicate numbers.

There are people and strange monkeys on this island, and you can not tell who is who (Edit: until you understand what they said - see below). They speak either only the truth or only lies.
Who are the following two guys?
A: B is a lying monkey. I am human.
B: A is telling the truth.