I recently got given a problem by a friend, which I have been struggling over for a while. It is this:
Draw 16 points, and 15 lines, with exactly 4 points on each line.
Can anyone help?
Place 15 points where the red dots are in the diagram. You then have 10 lines with four points on each, as shown. Now put the 16th point at the centre of the picture, where the blue dot is. You then get five more lines by joining the outer five red dots to the central dot.