I can write cow in 13 letters.

Can You?

10 people came into a hotel with 9 rooms and each guest wanted his own room. The bellboy solved this problem.
He asked the tenth guest to wait for a little with the first guest in room number 1. So in the first room, there were two people. The bellboy took the third guest to room number 2, the fourth to number 3, ..., and the ninth guest to room number 8. Then he returned to room number 1 and took the tenth guest to room number 9, still vacant.
How can everybody have his own room?

Find three whole, positive numbers that have the same answer when multiplied together as when added together.

What am I?

Find the next number in the series?
2, 12, 36, 80, 150, 252, 392, _ ?

I have a five and a three-gallon jar. Assuming there is an infinite supply of water, how can I measure one-gallon water?

I am quite hot but become too cold if you remove the first two letters. What am I?

There is a box full of marbles,
all but two are blue,
all but two are green,
and all but two are red.

How many marbles are in the box?

How can you drop a raw egg from a height onto a concrete floor without cracking it?

Replace the question mark with the correct number.