To do the method, begin by writing the two numbers you want to multiply at the top of two columns. In the left column, you progressively halve the number and take the integer floor of any “and a half” ...

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, ...