Andrew decorated 20 biscuits to take to a party. He lined them up and put icing on every second biscuit and different decorations on other biscuits. How many biscuits weren't decorated?
Find the Difference
Age 5 to 7 Challenge Level
You could use numbered counters that can be moved about if you're not using the interactivity.
Where might the largest number go?
You might find this sheet of blank pyramids useful.