How many words can a pen with half refill write?

John and Jacob are twin brothers. One of them is a liar whereas the other one is a truth-teller.

I called their home number and one of them picked up.
I asked. 'Does John lie?' The person replied with a yes.

Whom did I talk with, John or Jacob?

If an electric train is travelling south, then which way is the smoke going?

What number do you get when you multiply all of the numbers on a telephone's number pad?

He digs out tiny caves and stores gold and silver in them. He also built bridges of silver and made crowns of gold. They are the smallest you could imagine. Sooner or later everybody needs his help, yet many people are afraid to let him help them. Who is he?

If nine thousand, nine hundred nine dollars is written as $9,909,
how should twelve thousand, twelve hundred twelve dollars be written?

By using 'because' continuously three times, can you make an English statement ?

See the given image carefully. What you have to do is move the blue checkers in the position of the black checkers and vice versa. You are only allowed to move the checker to an adjacent empty space. Do it in the least possible moves.

Below the four parts have been reorganised. The four partitions are exactly the same in both arrangements. Why is there a hole?

Nine marbles are arranged in the image below. Can you slide two marbles to form a square?