What occurs twice in a week, once in a year but never in a day?

In front of you, there are 9 coins. They all look absolutely identical, but one of the coins is fake. However, you know that the fake coin is lighter than the rest, and in front of you is a balance scale. What is the least number of weightings you can use to find the counterfeit coin?

Where do fish keep their money?

You see me once in June, twice in November, and not at all in May. What am I?

Give it food and it will live; give it water and it will die.

If an electric train is travelling south, then which way is the smoke going?

I have no doors but I have keys, I have no rooms but I have space, you can enter but you can’t leave! What am I?

There are are five things wrong with this sentence; only geniuses will be able to to spot all of the mitstakes

Can you identify if it's a murder or a suicide ?

You are in a land where thirty men and two women were dressed in classic black and white dresses.
They begin to fight as soon as any of them move.

Where are you?