Whole Number & Decimal - Lesson 6 - Multiplication

The ‘Why’: Why does multiplication work the way it does?

This lesson starts with an exercise designed to get students to recognize that multiplication is a way of simplifying repeated addition. It is then followed by a refresher of the commutative and associative laws and why they work.

Similar to the addition and subtraction lessons, this is then split into mental and written techniques. Mental techniques covered include; doubles, using 10’s, hand tricks and partitioning. Students should be reminded that, whilst they may be able to answer quickly and another way, these are good techniques for them to have in their back pockets. The aim is to give a technique for as many time tables as possible. Each slide features an “I do, you do” example, followed by a time trail to see how many students can complete in one minute.

Following this is the written techniques that includes: bar models, grid method, lattice method and lines. Some of these descriptions are slight rewording of popular techniques. Grid method is the method by which the place value of each number is split and put in a table. The lattice method, is similar but features diagonal lines to give two digit answers followed by diagonal addition to give each place value. Lastly, line is the Japanese method of drawing a single line to represent each place value, followed by another line across is and then counting the points at which they cross.

The deliberate decision was made to not include column method as it will likely have been covered in primary and often leads students to an incorrect answer.

Towards the end of the lesson, there are some techniques for decimal multiplication including using similar sums and estimating followed by practice using any method. At the end is a mix of problem solving tasks including worded and spot the mistake problems.

Activities included:

• Repeated addition starter
• Commutative and associative law refresher
• Mental multiplication methods
• Written multiplication methods
• Decimal Multiplication
• Estimating and Using Similar Sums
• Mixed Problem solving