Proof by counter example is when an example that doesn't work disproves the conjecture. The tasks below offer opportunities to use proof by counter example. They form part of our Mastering Mathematics: Developing Generalising and Proof Feature.
problem
Five Steps to 50
Age
5 to 7
Challenge level
Use five steps to count forwards or backwards in 1s or 10s to get to 50. What strategies did you use?