The array can be shown as 5 groups of 3 showing that 5 x 3 = 15. Or it could be shown as 3 groups of 5 showing that 3 x 5 = 15. This demonstrates that multiplication is commutative. Image caption, ...

You can add or subtract numbers in lots of different ways. You can use number lines, number bonds, fact families, 10 squares and counters, or even just writing the numbers down. Sometimes it is faster ...