Saturday, January 30, 2010

10 Digit Number

A ten-digit number contains every digit from 0 to 9. The digits are arranged so that the number formed by the first two digits, reading from left to right, is divisible by 2, the number formed by the first 3 digits is divisible by 3, the first 4 by 4, and so on until the whole number is divisible by 10.

What is the number? There are two digits that can be placed immediately. Which are they?

Thursday, January 28, 2010

I am back :-} ...A simple puzzle to start with

I would like to start with a simple puzzle which I had come across recently. I guess this is a straight forward one... Give it a try :-}

4 criminals are caught and are to be punished. The Judge allows them to be freed if they can solve a puzzle. If they do not, they will be hung. They agreed.

The 4 criminals are lined up on some steps (shown in picture). They are all facing in the same direction. A wall separates the fourth man from the other three.

So to summarise :-
Man 1 can see men 2 and 3.
Man 2 can see man 3.
Man 3 can see none of the others.
Man 4 can see none of the others.

The criminals are wearing hats. They are told that there are two white hats and two black hats. The men initially don't know what colour hat they are wearing. They are told to shout out the colour of the hat that they are wearing as soon as they know for certain what colour it is.

They are not allowed to turn round or move.
They are not allowed to talk to each other.
They are not allowed to take their hats off.

Who is the first person to shout out and why?