The first person saw the bridge step on it and crossed,
the second person saw the bridge did not step on it but crossed,
the third person did not see the bridge did not step on it but crossed.
Who are these people?
The first box has two white balls. The second box has two black balls. The third box has a white and a black ball.
Boxes are labeled but all labels are wrong!
You are allowed to open one box, pick one ball at random, see its colour and put it back into the box, without seeing the colour of the other ball.
How many such operations are necessary to correctly label the boxes?
The word ladder puzzle was invented by Lewis Carroll, author of Alice’s Adventures in Wonderland.