Here is a classic one. The illustration below depicts nine dots in the form of a square. Draw four straight lines in such a way that each dot is crossed out.
You cannot cross a dot more than once.
You must not retrace any line.
You are not permitted to lift your pencil while drawing the lines.
Solution (Click to Show)
I first encountered this puzzle when my second-grade teacher challenged us to solve it. It took me less than a minute to solve it since it quickly occurred to me that he didn’t tell us it’s not permitted to draw the lines outside the dots. At first, I thought he would say that it’s not a valid solution, but he was surprised when I presented my answer to him. He then told me that I got the right answer.Perhaps, it was “thinking outside the dots” in action.