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

If you had a pizza with crust thickness 'a' and radius 'z', what's the volume of the pizza?

Can you figure out the logic I used to decide the order of the following words:
gun, shoe, spree, door, hive, kicks, heaven, gate, line, den

I am the beginning of the end, and the end of time and space. I am essential to creation, and I surround every place. What am I?

What demands an answer, but asks no questions

Can you find out the number that should replace the question mark with a valid reason?

A Shopkeeper collects 71 rupees in the form of 20 paisa and 25 paisa.
He collects a total of 324 coins.

Can you tell me how many number of 20-paisa and 25-paisa he got?

In a science lab, a petri dish hosts a healthy colony of yeast for an experiment. Now every minute, all the yeast cells divide into two. At noon, there was just a single cell of yeast and at 1:22, the Petri dish was half full. Can you calculate when the dish will be full of yeast?

What can go up a chimney down, but can’t go down a chimney up?

You have a 12 liters jug full of water. You have two empty 8 liters and 5 liters jug. How can you divide the water into two equal parts using these jugs?