The overarching key ideas of estimation, benchmarks, visualisation, equality and equivalence, language and strategies need to be considered when developing units of work in multiplication. The specific key ideas in multiplication are: equal groups, composite units and properties of multiplication. The properties of multiplication include: commutative property, associative property, distributive property, null-factor property, identity property and inverse property.
The quantity in each group is the same.
A composite unit is a collection of single items represented as one group.
Multiplication has several properties, which are outlined below.
The order in which two numbers are multiplied does not affect the product.
The order in which three or more factors are multiplied does not affect the product.
Factors can be partitioned, multiplied separately and the partial products are then added.
Multiplying a number by zero will always give a product of zero.
Multiplying a number by one will not affect the quantity.
Multiplication and division are related operations that undo each other, therefore division can be used to solve a multiplication problem.
The inverse property is applied to form fact families.
Multiplication equations have a multiplier (how many groups or sets of equal size), a multiplicand (size of the equal sets) and a product (total number).
The × symbol means ‘of‘ (as in equal 'sets' of) and the = symbol represents the equality (sameness) of 9 × 7 (nine 'sets' of seven objects) and 63 (objects).
Multiplication strategies are methods to solve mathematical problems. The strategies may be mental, written, digital or a mix of the three.
Mental strategies are calculations worked in one's mind and may involve using one of the following methods:
• partitioning and recombining numbers, using the distributive property
• rounding and adjustment strategies
• proportional adjustment strategies.
Written strategies are often algorithms, meaning they are step-by-step methods to find an answer. The most common algorithm for multiplication applies place-value structure and the distributive property and should only be introduced once students have explored a range of strategies and have developed a sound conceptual understanding of multiplication.
Multiplication is applicable in a range of settings. These settings are sometimes referred to as ‘problem types’. Table 1 provides some examples of problem types.
A factor is a whole number that divides exactly into another number.
A prime number is a whole number greater than one with exactly two factors: itself and one.
A composite number is a whole number that has factors other than one and itself (ACARA 2019).
A multiple is many groups of the same quantity.