Christina has four daughters, and each of her daughters has a brother. How many children does Christina have?

Suppose we lay down two cups in front of you. One of the cups is filled with tea and the other one with coffee. Now we ask you to take a spoonful of tea and mix it with the coffee. At this moment, the coffee cup has a mixture of tea and coffee. You have to take that mixture (spoonful) and add it back to the tea.

Can you now tell if the cup of coffee has more tea or the cup of tea has more coffee?

As shown in the image, the nine Dogs are square fenced. By constructing just two square fences can you make sure that two Dogs cannot meet each other without crossing the fence?

John killed hundreds of people mercilessly and yet the police were not able to put her behind the bars. Why?

What has many teeth, but cannot bite?

When my father was 31 I was 8. Now he is twice as old as me. How old am I?

What is the fewest number of coins that would be required in order to make sure each and every coin touches exactly three other coins?

Can you decipher these quotes by Albert Einstein?
Blf xzm mvevi hloev z kilyovn lm gsv ovevo lm dsrxs rg dzh xivzgvw.

I make a loud sound when I’m changing. When I do change, I get bigger but weigh less. What am I?

I am beautiful, up in the sky. I am magical, yet I cannot fly. To people I bring luck, and to some people, riches. The boy at my end does whatever he wishes. What am I?