How can you tell a raw egg from a hard-boiled egg?

A seven-year-old kid challenged his classmates that he can make the number one disappear by adding something to it.

How can he do that?

If 5 cats catch 5 mice in 5 minutes, how long will it take one cat to catch a mouse?

In an office's desk, you find a unique method that shows the current day of the month. Two numbered cubes are used to depict the current date.

Can you find out the numbers on both the cubes so that each date can be mentioned using them?

Please note that you have to use both the cubes to display any date. Thus the 1st day must be represented by 01 and so on.

You have an empty wine bottle with a cork that has been secured at the top in a normal way. There is a metal ring inside the bottle that is suspended by a string.

How can you make the metal ring drop to the bottom if you are not allowed to touch anything - not the bottle, not the cork, not the thread and not the ring?

You are trapped in a room with two doors. One leads to certain death and the other leads to freedom. You don't know which is which.
There are two robots guarding the doors. They will let you choose one door but upon doing so you must go through it.
You can, however, ask one robot one question. The problem is one robot always tells the truth, the other always lies and you don't know which is which.
What is the question you ask?

Two batsman each on 94 runs. Seven runs needed to win in last 3 balls. Both make 100*. How?

As we know that white starts the game of chess. Can you find the scenario shown in the picture below is possible when all the white pieces are at the original place while the black pawn is not as in the below picture?

A man dies of old age on his 25 birthday. How is this possible?

Use only one mathematical symbol and all numbers (0-9) to get a sum of 99