What is always in front of you but can’t be seen?

What is the four-digit number in which the first digit is one-third the second, the third is the sum of the first two, and the last is three times the second?

John is found dead in a bare field. Nobody killed John,
John did not commit suicide.

Inspector Jacob found a bag just a few meters away from John which could save his life. What was in the bag?

In particular commonwealth games, a female participant won silver and gold medals for a single event.

How can this be possible?

It belongs to you, but other people use it more than you do. What is it?

At a party, there are five people and a whole round cake lying at the centre of the table. Only four people will make a cut and take their piece and the last one will get the remaining piece on the table. How can they make sure that everyone gets a 1/5th of the piece?

The answer I give is yes, but what I mean is no. What was the question?

You walk into a room that contains a match, a kerosene lamp, a candle and a fireplace. What would you light first?

Replace the question mark with the correct number.

2 + 2= 4
3 + 3= 18
4 + 4= 48
5 + 5= ?

I have no doors but I have keys, I have no rooms but I have space, you can enter but you can’t leave! What am I?