Double-Digit Multiplication

To multiply a two-digit number by another two-digit number, you can split the numbers into tens and ones and then add the parts together. For example, 12 × 13 can be worked out as 10 × 13 plus 2 × 13, which gives 130 plus 26, so the answer is 156.

Splitting numbers into parts is the basis of many fast methods for mental multiplication. The same idea is used in the area model, which shows each part as a rectangle.