The key idea of number strategies at level 3 is that numbers can be partitioned and combined to solve more complex addition and subtraction and simple multiplication and division problems.

At level 3 students are able to apply a range of strategies to solve addition and subtraction problems including larger numbers and problems that involve multiple steps. There are a number of strategies that involve part-whole thinking at this level. These include:

- Compensation: For example, to solve 53 – 28; 53 – 30 = 23, 23 + 2 = 25.
- Reversibility: For example, to solve 43 – 38; solve as 38 + ? = 43.

At this level students are also able to derive simple multiplication facts from known facts. For example, if they know 5 x 5 = 25, they would be able to use this to work out that 5 x 6 = 30.

Further information on number strategies can be found in the books supporting the Numeracy Development Projects.

This key idea develops from the key idea of number strategies at level 2 where students can partition and combine numbers to solve simple addition and subtraction problems.

This key idea is extended in the key idea of number strategies and knowledge at level 4 where students can represent and operate on rational numbers in a variety of ways.