What is the below Rebus indicate?

What number divided by 4 is the same as that number minus 4?

I have nine bottles of wine and one of the nine bottles is poisoned.
I need to find the poisoned bottle with two facts
(1) Poison is deadly, only a sip will cost death
(2) I have two mice to do so.

How should I do 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?

How is the moon similar to a dollar?

Astrology starts with the alphabet A, Biology starts with B, Psychology with P and Limnology with L.

Can you find an "ology" that begins with a P?

What is the centre of gravity?

Can you find a five letter word that is left with only two letters if one is removed?

Which fur should we be getting from the Lion?

A man dies of old age on his 25 birthday. How is this possible?