How many letters are in the alphabet?

The more of this there is, the less you see. What is it?

Can you find the next number in the below sequence
3 , 7 , 10 , 11 , 12 , 17 ?

There is so small cabin inside a deep forest.
All the forest burned out to worst possible but the inside of the cabin is still the same.
However all the person inside the cabin die.

How come ?

Find the Next Number in the Sequence

2 9 3 1 8 4 3 6 5 7 ?

You need to climb ten stairs. At every stair, you can either take one step up or you can jump two steps up.

In how many different ways you can climb 10 stairs?

There are 20 people in an empty, square room. Each person has full sight of the entire room and everyone in it without turning his head or body, or moving in any way (other than the eyes). Where can you place an apple so that all but one person can see it?

The first box has two white balls. The second box has two black balls. The third box has a white and a black ball.

Boxes are labeled but all labels are wrong!

You are allowed to open one box, pick one ball at random, see its colour and put it back into the box, without seeing the colour of the other ball.

How many such operations are necessary to correctly label the boxes?

It belongs to you, but other people use it more than you do. What is it?

It is deaf, Dumb and Blind!!!

Still, always tells the truth. What is it?