Can you find out the remainder when 3^300 is divided by 5?

Can you find out a way through which you can make five squares out of the given figure by moving just six match sticks?

What number when divided in half becomes zero?

The host of a game show offers the guest a choice of three doors. Behind one is an expensive car, but behind the other two are goats.
After you have chosen one door, he reveals one of the other two doors behind which is a goat (he wouldn't reveal a car).

Now he gives you the chance to switch to the other unrevealed door or stay at your initial choice. You will then get what is behind that door.

You cannot hear the goats from behind the doors, or in any way know which door has the prize.

Should you stay, or switch, or doesn't it matter?

I know a nine-letter word having only one vowel.
Do you ?

I shave every day, but my beard stays the same. What am I?

You knock a Table over in the library, and suddenly 20 eyes are looking at you.

What is the next number in this matchsticks series riddle?

What can run but never walks, has a mouth but never talks, has a head but never weeps, has a bed but never sleeps?

What building has the most stories?