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

I cry without having a voice.
I fly without having wings.
I bite without having teeth.
I whisper without a mouth.

Who am I?

Things are just as they seem, right? Well, check again.
Can you count the number of tigers in this picture ?

I never stop running even when I standstill. If I am formed by joining two identical bodies together, can you guess who I am?

Find the next number in the sequence

1, 2, 6, 21, 88, __?

Can you start the fire using two pieces of wood?

On my way to St. Ives I saw a man with 7 wives. Each wife had 7 sacks. Each sack had 7 cats. Each cat had 7 kittens. Kittens, cats, sacks, wives. How many were going to St. Ives?

What has many keys but can’t open a single lock?

You have a basket containing ten apples. You have ten friends, who each desire an apple. You give each of your friends one apple.
Now all your friends have one apple each, yet there is an apple remaining in the basket.
How?

Nine marbles are arranged in the image below. Can you slide two marbles to form a square?