What word begins and ends with an E, but has only one letter?

Can you replace the question mark with the correct number?

You stand in front of two doors. A guard stands next to each door. You know the following things: one path leads to paradise, the other leads to death. You cannot distinguish between the two doors. You also know that one of the two guards always tells the truth and the other always lies. You have permission to ask one guard one question to discover which door leads to paradise. What one question would you ask to guarantee you enter the door to paradise?

Christina is practising her dance steps along with her friends. In a particular sequence, all of them form a row. At that point, Niharika is standing in the 4th position from either end of the row.
Can you find out how many girls are practising together?

A man is found unconscious in front of a store at two in the morning. His head is bleeding and there’s a brick laying next to him. When the police arrive, they carry the man to jail. Why did they arrest him?

A prisoner is told: "If you tell a lie, we will hang you and if you tell the truth, we will shoot you." What did the prisoner say to save himself?

What has one letter and starts with an E?

John was working on a Chemical Mixture whose weight comprise 90% liquid and 10% solid. The total weight of the mixture is 20 pounds. After a while, John noticed that some of the liquid evaporated and now the liquid comprises just 50% of the weight.

What is the weight of the chemical mixture now?

Do you know of a place where the wind blows south and then suddenly shifts direction towards the north?

I have cities, but no houses. I have mountains, but no trees. I have water, but no fish. What am I?