Who always enjoys poor health?

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

Why is 6 afraid of 7?

I am sure no one can have two things for dinner. what are they?

Using eight eights and addition only, can you make 1000?

What does below science rebus mean?

Ag Ag Ag
Ag SPOON Ag
Ag Ag Ag

It's a 7-letter word.
If we remove 1 letter from it, it remains the same.
If we remove 2 letters from it, it remains the same.
If we remove 3 letters from it, it remains the same.
If we remove all the letters from it, still it remains the same.
What is it?

What numbers should go on the bottom line?
3 6 9 15
8 2 10 12
11 8 19 27
19 10 29 39
? ? ? ?

Which wheel of car does not rotate when you turn your car right?

I am under you when I am whole.
I shift above you if you remove the first letter.
I come all around you if you remove the second as well.

Can you tell me who I am?