what does this picture(rebus) riddle means ?

I have lakes with no water, mountains with no stone and cities with no buildings. What am I?

There was once a college that offered a class on probability applied to the real world. The class was relatively easy, but there was a catch. There were no homework assignments or tests, but there was a final exam that would have only one question on it. When everyone received the test paper it was a blank sheet of paper with a solitary question on it: 'What is the risk?'.Most students were able to pass, but only one student received 100% for the class! Even stranger was that he only wrote down one word!
What did he write?

Count the Triangle in the figure given below:

Can you fill the blank with the correct number?

6 30 870 756030 _____

What's the only room from which no one can enter or leave

What you cannot hold but it is yours?

What has 13 hearts but no other organs?

There are a number of books on a shelf. If one book is the 4th from the left and 6th from the right, how many books are on the shelf?

If eleven plus two equals one, what does nine plus five equal?