This activity can be presented to the children when reinforcing single digit addition. It is also an opportunity for children to practice number bonds using three numbers.

To enable the children to adjust their solutions and try different combinations of numbers, provide counters or bingo number discs with the digits 1 through 6 written on.

The first line will be easy to complete but the challenge comes as children try to complete all three lines of the triangle. This will lead to a discussion of why a line doesn't work, what might be a solution to the difficulty and what the implications are when a digit is moved. Working with lower totals to begin with allows the children to develop strategies for placing the low and high digits that can be tested with triangles that have greater totals.

Have children create their own problems by using a different sequence of numbers. They should make discs showing the numbers they have chosen and work out the solutions before setting the challenge for a friend. This is another opportunity to test their hypothesis from the fist set of problems. Will the original strategies work with another sequence of numbers?