How many sides does a circle have?

Can you fill the blank with the correct number?

6 30 870 756030 _____

Buy me, smell me or deliver me, I do not change.

Who am I?

See the given image carefully. What you have to do is move the blue checkers in the position of the black checkers and vice versa. You are only allowed to move the checker to an adjacent empty space. Do it in the least possible moves.

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?

The following four words might seem abrupt to you. But you can make them meaningful by just adding vowels.
RDSH
GGPLNT
TMT
NN

Hint: All of them are vegetables.

In the given figure, you can see that four match sticks are used to form a square. Can you form five squares by using six matches?

Imagine a box with two cogwheels, one big with 24 teeth and one small with 8 teeth. The big one is firmly attached to the center of the box which means it does not turn or move while the small one rotates around the big one.

How many times do you think that the smaller wheel will turn compared to the box when it turns once around the big one?

If "P" means "-", "Q" means "/", "R" means "+", and "S" means "*" then find the value of the following:

21 Q 7 R 9 S 10 P 13

The horse jumps over the king.
Strangely there is absolutely no scratch on him.

Can anyone explain, how is this possible?