Can you convert the number zero(0) into a positive number using just one mathematical operator ?

You are in a room that has three switches and a closed door. The switches control three light bulbs on the other side of the door. Once you open the door, you may never touch the switches again. How can you definitively tell which switch is connected to each of the light bulbs?

What brings you down but never up?

A crime was committed at baker street. Ibrahim Dakota who was shot in the stomach was the main suspect. Sherlock questioned the suspect. The conversation started as:
Sherlock: What's your story, Ibrahim?
Ibrahim: I was walking around baker street and suddenly a man from the back shot me. I ran as fast as I could to save my life".
Sherlock: That is enough (and ask the police to arrest him).

Why does Sherlock think he is the murderer?

Can you start the fire using two pieces of wood?

Which tank will fill first?

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

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

You walk into a room and see a bed. On the bed, there are two dogs, five cats, a giraffe, six cows, and a goose. There are also three doves flying above the bed. How many legs are on the floor?

What's the next in the series?

H, Be, F, S, Mn, Kr, In, Gd, Tl, ?