What is the fastest way to double your money?

After teaching his class all about Roman numerals (X = 10, IX=9 and so on) the teacher asked his class to draw a single continuous line and turn IX into 6. The teacher's only stipulation was that the pen could not be lifted from the paper until the line was complete.

Replace each alphabet with the number (1-9) to make the below equation correct.

AB * C = DE - F = GH / I

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

Many have heard it, but nobody has ever seen it, and it will not speak back until spoken to. What is it?

In two decks of cards, what is the least amount of cards you must take to be *guaranteed* at least one four-of-a-kind?

The more you take me, the more you leave me behind.
Who Am I?

Why is the Hole below a Lock?

Eight of us go fourth, not back, to protect our king from an attack. What are we?

In a boat, the father of a sailor's son is sitting with the son of the sailor. However, the sailor is not present on the boat.

Can this even be possible?