Simple riddles

I have all the knowledge you have. But I am small as your fist that your hands can hold me. Who am I?

You have to look at me to say what I show you. I offer two different purposes but I am spelled the same and I am pronounced the same.

My best buddy always makes mistakes. But I would easily get rid of the mistakes. What Am I?

There are several chickens and rabbits in a cage (with no other types of animals). There are 72 heads and 200 feet inside the cage. How many chickens are there, and how many rabbits?

I have four legs. I live in Africa. I am big and grey. I live in the river. What am I?

It can be cracked, it can be made, It can be told, it can be played. What is it?

What goes up when rain comes down?

They are twin sisters, same height; they work in the kitchen, arm in arm. Whatever is cooked, they always try it first.

What is everthing yet nothing, has no start and no end, creates yets destroys, brings life and death what is it?

A man wanted to enter an exclusive club but did not know the password that was required. He waited by the door and listened. A club member knocked on the door and the doorman said, "twelve." The member replied, "six " and was let in. A second member came to the door and the doorman said, "six." The member replied, "three" and was let in. The man thought he had heard enough and walked up to the door. The doorman said ,"ten" and the man replied, "five." But he was not let in. What was the right answer then?