Why do people go to bed?

Two guards were on duty outside a barracks. One faced up the road to watch for anyone approaching from the North. The other looked down the road to see if anyone approached from the South. Suddenly one of them said to the other, "Why are you smiling?"

How did he know his companion was smiling?

While going to your grandmother's house, you counted Twenty houses on the right side. While returning back to your home, you counted Twenty houses on the left side.

How many houses are there between your home and your grandmother's home?

When can we add 2 to 11 and get 1 as the correct answer?

Name a key which is hardest to turn.

It is a nine-letter word.
The exact opposite of the phrase "friendly and outgoing"
It contains the word "over".
It starts will a vowel.

What is it?

What three numbers, none of which is zero, give the same result whether they’re added or multiplied?

Can you count the number of squares in the figure below?

13 decks of cards have been mixed. What is the minimum number of cards that must be taken out from the above-mixed cards to guarantee at least one 'four of a kind?

In 1990, a person is 15 years old. In 1995, that same person is 10 years old. How can this be?