The key idea of number strategies at Level 2 is that numbers can be partitioned and combined to solve simple addition and subtraction problems.
At level 2 students have begun to recognise that numbers are abstract units that can be either treated as wholes or partitioned and recombined. This is called part-whole thinking and represents a significant developmental step in a student’s understanding of number. Part-whole thinking can be applied to derive results from known facts, such as finding addition answers by using doubles or teen numbers. There are a number of strategies that involve part-whole thinking at this level. These include:
- Compensation from known facts: For example, to solve 7 + 6; 6 + 6 = 12, so 7 + 6 = 13.
- Place value partitioning: For example, to solve 23 + 13; (20 + 10) + (3 + 3) = 30 + 6 = 36
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 1 where students rely on counting to solve number problems.
This key idea is extended in the key idea of number strategies at level 3 where students can partition and combine numbers to solve more difficult addition and subtraction problems, as well as simple multiplication and division problems.