what does this picture(rebus) riddle means ?

I come in different shapes and sizes.
Parts of me are curved, other parts are straight.
You can put me anywhere you like,
but there is only one right place for me.
What am I?

Can you divide the below-given shape into four equal and identical pieces?

Can you replace the question mark with the correct number?

How many times in a given day, minutes and hour clock comes in a straight line ?

I went to the bookshop and spent one-half of the money that was in my purse.

When I came out, I found that I had as many cents as I had dollars and half as many dollars as I had cents when I went in. Find the money in my purse when I entered the store.

You measure my life in hours
I serve you by expiring
I vanish faster when I am thin
and slower when I am thick
The wind is my energy
What am I?

I have no doors but I have keys, I have no rooms but I have space, you can enter but you can’t leave! What am I?

What question can you never answer yes to?

Prove that twice of ten is the same as twice of eleven.