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

My first is in chocolate but not in ham. My second is in cake and also in jam. My third at tea time is easily found. Altogether, this is a friend who is often around. What is it?

When you say goodbye, I am what you need to tie.
I come as a couple and go wherever you run.
Who am I?

There are 2 sand hourglasses.

The small one can measure 5 hours and the large one can measure 7 hours.

How can we measure 16 hours with 2 sand hourglasses running together ?

In a concert, Christina is performing a dance show with her group.
At 10:00, she and her crew were dancing in an absolutely straight line. At that time Christina was standing in 4th position from both the front and back end of the row.

What was the size of her crew?

How many words can a pen with half refill write?

What is full of holes but still holds water?

A man dies of old age on his 25 birthday. How is this possible?

What always comes into a house through the keyhole?

What four weights can be used to balance from 1 to 30 pounds?