If we add four times the age of John four years from now to five times his age five years from now we get ten times his current age.

How old will John be two years from now?

Can you decipher the two rows to find the hidden word?

Find the next number in the series below.

6 18 270 72090 ?

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.

A train full of passengers goes through a tunnel. When the train comes out from the other end, there is no single person on the train.

How did it happen?

what's the probability of getting a king or a queen from a pack of 52 cards?

why number 8549176320 is one of a kind?

Can you find out the remainder when 3^300 is divided by 5?

I cry without having a voice.
I fly without having wings.
I bite without having teeth.
I whisper without a mouth.

Who am I?

Look at this sequence from top to bottom. What is the next number in the sequence?
1
11
21
1211
111221
312211