It walks on 4 when its young, walks on 2 when it's older, and walks on 3 when its very old?

Look at this sequence from top to bottom. What is the next number in the sequence?
1
11
21
1211
111221
312211

If I remove one from eleven it becomes Ten and if I remove one from nine also becomes Ten. How?

Solve the equation in the image by looking at the pattern closely.

I am the fastest animal but cannot climb the tree. What am I?

At a party, there are five people and a whole round cake lying at the centre of the table. Only four people will make a cut and take their piece and the last one will get the remaining piece on the table. How can they make sure that everyone gets a 1/5th of the piece?

A man looks at a painting in a museum and says, “Brothers and sisters I have none, but that man’s father is my father’s son.” Who is in the painting?

Alex opened 24 presents
Jonah opened 8 presents
Clara opened 1 present

Can you find out how many presents were opened by Candy?

What number when divided in half becomes zero?

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?