A man lives on the fifteenth floor of an apartment building. Every morning he takes the elevator down to the lobby and leaves the building. In the evening, he gets into the elevator, and, if there is someone else in the elevator, or if it was raining that day, he goes back to his floor directly. Otherwise, he goes to the tenth floor and walks up five flights of stairs to his apartment. Can you explain why he does this?

The picture shows the dice results in each couple of throws. If they are actually following a pattern, can you find out the missing one?

Name a key which is hardest to turn.

A man has a barrel filled with oil that weighs 100 pounds, and then he puts something into it. Now the barrel weighs less than 100 pounds. What did he put in the barrel?

What is the word or phrase?

You see a boat filled with people, yet there isn’t a single person on board. How is that possible?

What is black when you buy it, red when you use it, and gray when you throw it away?

There are 100 bulbs in a room. 100 strangers have been accumulated in the adjacent room. The first one goes and lights up every bulb. The second one goes and switches off all the even-numbered bulbs - second, fourth, sixth... and so on. The third one goes and reverses the current position of every third bulb (third, sixth, ninth? and so on.) i.e. if the bulb is lit, he switches it off and if the bulb is off, he switches it on. All the 100 strangers progress similarly.

After the last person has done what he wanted, which bulbs will be lit and which ones will be switched off?

How high do you have to count before you use the letter “a” in the English spelling of the whole number?

A man in a car saw a Golden Door, Silver Door and a Bronze Door. What door did he open first?