Find the Next Number in the Sequence

2 9 3 1 8 4 3 6 5 7 ?

I am taken from a mine and shut up in a wooden case, from which I am never released, and yet I am used by almost every person. What am I?

If an electric train is travelling south, then which way is the smoke going?

Before Mount Everest was discovered, what was the highest mountain in the world?

You can see it everyday, But cannot touch it at will. What is it?

When I get multiplied by any number, the sum of the figures in the product is always me. What am I?

There is a box. The area of its top is 240 square units, the area of the front is 300 square units and the area of the end is 180 square units.

Can you calculate the dimensions of this box with the given data?

You are trapped in a room with two doors. One leads to certain death and the other leads to freedom. You don't know which is which.
There are two robots guarding the doors. They will let you choose one door but upon doing so you must go through it.
You can, however, ask one robot one question. The problem is one robot always tells the truth, the other always lies and you don't know which is which.
What is the question you ask?

using four eights (8) and a one (1) and one mathematical symbol , create the number 100

I travel all around the world but always stay in the corner. What am I?