Find three whole, positive numbers that have the same answer when multiplied together as when added together.

What's the next in the series?

H, Be, F, S, Mn, Kr, In, Gd, Tl, ?

A tree doubled in height each year until it reached its maximum height over the course of ten years. How many years did it take for the tree to reach half its maximum height?

There are a number of books on a shelf. If one book is the 4th from the left and 6th from the right, how many books are on the shelf?

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.

Lifeless eyes on my smiling face and watch your child's sleeping place. In their dreams they hold me tight. What am I?

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

Two-person want to cross a river. Only one boat is present on the riverside that can carry only one person at a time.

However, they still manage to cross the river. How is it possible?

What number when divided in half becomes zero?

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?