Take 9 from 6, 10 from 9, 50 from 40, and leave 6.

How Come ??

There are people and strange monkeys on this island, and you can not tell who is who (Edit: until you understand what they said - see below). They speak either only the truth or only lies.
Who are the following two guys?
A: B is a lying monkey. I am human.
B: A is telling the truth.

What is the fewest number of coins that would be required in order to make sure each and every coin touches exactly three other coins?

What does it mean?

If a shopkeeper can only place the weights on one side of the common balance. For example, if he has weights 1 and 3 then he can measure 1, 3 and 4 only. Now the question is how many minimum weights and names of the weights you will need to measure all weights from 1 to 1000? This is a fairly simple problem and very easy to prove also.

What has hands, but can’t clap?

A certain street contains 100 buildings. They are numbered from 1 to 100. How many 9's are used in these numbers?

Quickly Solve this riddle

7 - 4 + 3 * 0 + 1 = ?

The captain of a ship was telling this interesting story: "We travelled the sea far and wide. At one time, two of my sailors were standing on opposite sides of the ship. One was looking west and the other one east. And at the same time, they could see each other clearly." How can that be possible?

Why do we preferably have round manhole covers and not square ones?