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

Analyze and find the missing item in the sequence:
16, 06, 68, 88, __, 98

Can you circle exactly four of these numbers such that the total is twelve?

1 6 1
6 1 6
1 6 1
6 1 6

You know three triplets: Frank John and Wayne (need to return your money). Frank always tells the truth while John and Wayne always lie. You meet one of them on the road and can ask him a three-word question.
Which question, will you ask?

Can you write down eight eights so that they add up to one thousand?

I know a 5-digit number having a property that With a 1 after it, it is three times as large as it would be with a one before it.

Guess the number?

You need to pick one entry from pot A and one from pot B to have a perfect match. Can you do it?

In one of the popular batman series movie "Batman Forever", there was a riddle that goes like "Tear me off and then scratch my head and I was red then and now I am back. Who am I?

One is to three as three is to five and five is to four and four is the magic number.
What is the pattern?

Buy me, smell me or deliver me, I do not change.

Who am I?