Step 3 Objective

Use a range of strategies when solving problems.


What if pupils find this a barrier?

diagram showing three lines crossing

Line Crossings

  • Draw three straight lines (line segments) so that some cross over each other.
  • How many crossings are there?
  • Try different arrangements of the lines. What is the maximum number of possible crossings?
  • Try using more lines.
  • Is there a rule for the maximum for any number of lines? If so, write it down.

Use the problem Line Crossings.

  • In this diagram you have three (or four or ...) lines - how many crossings are there?
  • If you add another line to the diagram how many crossings will there be now? Will it be more, the same or fewer?
  • Explain why you think so?
  • Draw another line. What do you notice?