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?

A blonde put eyeliner on her head. Why?

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

What does below Rebus mean ?

esgg sgeg gegs gsge

Two old friends, Jack and Jill, meet after a long time, and discussing as:

Jack: Hey, how are you, man?

Bill: Not bad, got married and I have three kids now.

Jack: That's awesome. How old are they?

Bill: The product of their ages is 72 and the sum of their ages is the same as your birth date.

Jack: Cool..But I still don't know.

Bill: My eldest kid just started taking piano lessons.

Jack: Oh, now I get it.

How old are Bill's kids?

How many Watermelons are there in the below picture?

As you can see that fifteen matches have been used to form an arrangement. What you have to do is remove any six of them to make them ten.

John is asked to stand behind Jacob and Jacob is asked to stand behind John. Both of them feel confused about it and don't know what to do?

But it is quite possible, do you know how?

You are in a room with no metal objects except for two iron rods. Only one of them is a magnet.
How can you identify which one is a magnet?