There are a number of books on a shelf. If one book is the 4th from the left and 6th from the right, how many books are on the shelf?

Find a 9-digit number, which you will gradually round off starting with units, then tenth, hundred etc., until you get to the last numeral, which you do not round off. The rounding alternates (up, down, up ...). After rounding off 8 times, the final number is 500000000. The original number is commensurable by 6 and 7, all the numbers from 1 to 9 are used, and after rounding four times the sum of the not rounded numerals equals 24.

Can you find the thief by just looking at the picture below?

What does below Rebus say?

XLR8

Two natural numbers have a sum of less than 100 and are greater than one.

John knows the product of the numbers and Jacob knows the sum of numbers.

The following conversation takes place between them:
John: 'I am not aware of those numbers.'
Jacob: 'I knew you wouldn't be. I am not aware myself.'
John: 'Now I know them!'
Jacob: 'Now I know them, too!'

What are the two numbers?

Look at the picture and find out which square is not linked with any of the other squares.

Can you place three balls such that the equation shown in the picture holds true?

A man says, "Brothers and sisters, have I none, but that man's father is my father's son." Who is that man?

Can you make a six-letter word using the letters N, A and B ?

John was drowned by he was not wet. How?