10+10 and 11+11 can give you the same answer.

Explain how?

Once upon a time, there was a castle on a square island. The entire island was surrounded by a 14m wide trench. The Romans had wanted to invade the castle and had brought a few wooden planks along with them to facilitate themselves in crossing the moat. The planks were however found to be only 13m long.

The Romans still managed to cross the trench. How did they do it?

How far can you walk into the woods?

100 prisoners are stuck in the prison in solitary cells. The warden of the prison got bored one day and offered them a challenge. He will put one prisoner per day, selected at random (a prisoner can be selected more than once), into a special room with a light bulb and a switch which controls the bulb. No other prisoners can see or control the light bulb. The prisoner in the special room can either turn on the bulb, turn off the bulb or do nothing. On any day, the prisoners can stop this process and say "Every prisoner has been in the special room at least once". If that happens to be true, all the prisoners will be set free. If it is false, then all the prisoners will be executed. The prisoners are given some time to discuss and figure out a solution. How do they ensure they all go free?

What is the largest amount of money that you can possess in change and still if someone asks you for a dollar, you won't be able to give?

I taste better than I can smell. Who am I?

Do You See It?

I have no life, but I can die. What am I?

Our product and our sum always give the same answer. Who are we?

My friends called me Iron59 because my parents are a chemist and a mathematician. What is my real name?