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

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?

Take number 1000 and then add 20 to it.
Now add 1000 one more time.
Now add 30.
Now add 1000 one more time.
Now add 40.
Now add 1000 one more time.
Now add 10.

What is the total?

What has lots of eyes, but can’t see?

What kind of band never plays music?

What does below rebus means ?

What has six faces, but does not wear makeup, has twenty-one eyes, but cannot see? What is it?

John left on a horse on Thursday , was gone for two days, and came back on Thursday after completing his work. How did that happen?

I have no doors but I have keys, I have no rooms but I have space, you can enter but you can’t leave! What am I?

Forwards I am heavy, backward I am not. What am I?