New
New
Year 6

Explain how to use the associative law to multiply efficiently

I can explain how to use factorisation and the associative law to multiply efficiently.

New
New
Year 6

Explain how to use the associative law to multiply efficiently

I can explain how to use factorisation and the associative law to multiply efficiently.

Lesson details

Key learning points

  1. Multiplication can be simplified by factorising one of the factors.
  2. Look at the factors to identify which are composite numbers.
  3. Composite numbers can be factorised.
  4. Multiplication is commutative.
  5. Factors can be grouped in different ways and the product remains the same.

Keywords

  • Associative law - The associative law states that it doesn't matter how you group or pair values (i.e. which we calculate first), the result is still the same. It applies for addition and multiplication.

  • Composite number - A composite number is an integer with more than two factors. All integers greater than 1 are either composite or prime.

Common misconception

Pupils can identify factors of a 2-digit number but do not consider efficiency when multiplying.

Draw attention to factor pairs and those which result in easier calculations e.g. pupils often find multiplying by 4 or 5 easier than 7, or can apply doubling when multiplying by 2

This lesson assumes pupils are familiar with and increasingly fluent in recall of factors of 2-digit numbers. Consider how you might scaffold the learning if required in order to focus attention on the strategy for multiplication.
Teacher tip

Equipment

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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6 Questions

Q1.
Select the prime numbers.
Correct answer: 3
Correct answer: 7
9
Correct answer: 11
15
Q2.
Look at the long multiplication below, what is the missing partial product?
An image in a quiz
Correct Answer: 28,152
Q3.
Select the numbers that are factors of 12
Correct answer: 1
Correct answer: 3
5
8
60
Q4.
Which of these is the complete list for the factors of 16?
2, 8
1, 2, 8, 16
Correct answer: 1, 2, 4, 8, 16
Q5.
What is the missing factor of 72? 1, 2, 3, 4, 6, 8, 9, 12, , 24, 36, 72
Correct Answer: 18
Q6.
Sam and Andeep are estimating the total number of visitors across the 35 Olympic venues on one day. Each venue has on average 6,012 visitors per day. How many visitors on average, visited on this day?
Correct Answer: 210,420

6 Questions

Q1.
Look at the numbers below and select the prime numbers.
Correct answer: 23
24
27
28
Correct answer: 29
Q2.
Select the composite numbers.
23
Correct answer: 25
41
Correct answer: 42
Correct answer: 55
Q3.
Which of these are ways that 14 could be represented with its factors?
Correct answer: 2 and 7
Correct answer: 1 and 14
7 and 7
3 and 11
Q4.
Select the expressions that are equivalent to 23 × 3 × 9
Correct answer: 3 × 23 × 9
Correct answer: 9 × 3 × 23
6 × 3 × 23
23 × 27
Q5.
Select the expressions that are equivalent to 24 × 18
24 × 1 × 17
Correct answer: 24 × 2 × 9
Correct answer: 24 × 3 × 6
24 × 3 × 15
Q6.
Look at the equation. Find the missing number. 29 × 33 = 29 × 3 × .
Correct Answer: 11