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?

Spot 5 differences in two Christmas tree below:

If there are fifteen crows on a fence and the farmer shoots a third of them, how many crows are left?

A certain street contains 100 buildings. They are numbered from 1 to 100. How many 9's are used in these numbers?

This puzzle is for Harry Potter fans. Do you know why Tom Riddle is called Lord Voldemort?

What type of tree can I carry in my hand?

What is the next number in this series?

4,12,84,3612....

You have 1023 apples and 10 bags. You have to distribute these apples in these 10 bags in any way you choose. But when I ask for a certain number of apples you have to give them in terms of bags without transferring the apples from other bags. How do you distribute the apples?

Two friends were stuck in a cottage. They had nothing to do and thus they started playing cards. Suddenly the power went off and Friend 1 inverted the position of 15 cards in the normal deck of 52 cards and shuffled it. Now he asked Friend 2 to divide the cards into two piles (need not be equal) with equal number of cards facing up. The room was quite dark and Friend 2 could not see the cards. He thinks for a while and then divides the cards in two piles.

On checking, the count of cards facing up is same in both the piles. How could Friend 2 have done it ?

It's a protector.
It sits on a bridge.
One individual can see directly through it, while others wonder what it hides.

What is it?