Years 5 - 8

Rael Picot, Meg Weily, Jackie Healey, Margate Primary School

This page would be more informative
with a photo from your classroom.


  1. Remove all the red plugs from a board and put them in the bag.
  2. Allow yellow/blue plugs to 'protect' like the Queens in chess, that is they can 'cover' any number of places forwards, backwards, left, right or diagonally from their current position.
For example the 'Queen' in this diagram protects all the holes shown by the arrows.
  • What is the minimum number of 'Queens' needed to protect the whole board?
    (We did it with 3 - can you?)
One way of keeping track of the protected holes is to fill them with blue plugs.

You can also keep a record on Poly Plug Paper.


  1. Gather more red boards and remove 6 x 6 plugs. Try the challenge again.
  2. Try the challenge again for 7 x 7 and 8 x 8 boards.

Calculating Changes ... is a division of ... Mathematics Centre