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

By moving exactly three matchsticks can you make the below equation true.It can be solved by 3 ways.

If "P" means "-", "Q" means "/", "R" means "+", and "S" means "*" then find the value of the following:

21 Q 7 R 9 S 10 P 13

What number comes next in the series?

5 15 5 18 5 24 14 20 _

I have feet, but no legs. Which animal Am I?

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

A man plots the murder of his wife. His plan is full proof. Nobody saw them leaving their house. He stabbed her with a knife while driving. She died on the spot. He threw her body in a valley. He threw the knife carefully wiping his finger prints on a random garbage bin. Then he went back to his home and no one was watching him this time as well.

After an hour, he was called by the local police department who informed him that his wife was murdered. They asked him to reach the scene of crime immediately. But as soon as he arrived at the crime scene, he was arrested by them.

How did the police know that he himself is the murderer?

You board a train. The train will have to enter a tunnel soon. You are claustrophobic. Which place is the best for you to sit?

You have a 12 liters jug full of water. You have two empty 8 liters and 5 liters jug. How can you divide the water into two equal parts using these jugs?

Forwards I am heavy, backward I am not. What am I?