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Year 5

Explain how to use the factor pairs of 100 to solve calculations efficiently

I can explain how to use the factor pairs of 100 to solve calculations efficiently.

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New
New
Year 5

Explain how to use the factor pairs of 100 to solve calculations efficiently

I can explain how to use the factor pairs of 100 to solve calculations efficiently.

Download all resources
Share activities with pupils

Lesson details

Key learning points

  1. Scales are often marked in factors of 100
  2. Rearranging calculations to make use of factors of 100 can simplify them

Common misconception

Pupils decompose the wrong factor therefore find it difficult to find a pair of factors that are equal to 100

Scaffold pupil's thinking when they begin to tackle a 2 digit by 2 digit calculation. Encourage them to ask questions of the numbers, for example: 'Is one of the numbers I have to start with a factor of 100?'

Keywords

  • Factor - Factors are whole numbers which exactly divide another whole number.

  • Commutative - The commutative law states that you can write the values of a calculation in a different order without changing the calculation; the result is the same. It applies for addition and multiplication.

  • Associative - 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.

Be sure to make connections back to pupils' learning in year 3 when they explored the common partitions of 100. This will be helpful as they make connections between the representations and how these are recorded as multiplicative equations.
Teacher tip

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).

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Starter quiz

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6 Questions

Q1.
A factor is:
always the number after the equals sign.
Correct answer: something that multiplies with another number.
the first number in a division equation.
the first number in a division equation. can be used in addition.
Q2.
Write down the missing factor from this factor bug.
An image in a quiz
Correct Answer: 5
Q3.
Which parts of a division equation can represent factors?
Correct answer: Quotient
Correct answer: Divisor
Dividend
Product
Q4.
Tick the equations that are true.
Correct answer: 25 × 4 = 100
100 = 25 × 5
Correct answer: 100 ÷ 2 = 50
25 = 100 ÷ 4
Correct answer: 10 × 10 = 100
Q5.
Apply the associative law to complete this calculation. 36 × 2 × 5 =
Correct Answer: 360
Q6.
Tick the calculation that could be represented as 5 × 2 × 31
31 × 20
52 × 31
81 × 2
231 × 5
Correct answer: 62 × 5

Exit quiz

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6 Questions

Q1.
Tick the factor pairs of 100
2 and 20
4 and 50
Correct answer: 5 and 20
Correct answer: 50 and 2
25 and 5
Q2.
Write down the missing factor in this factor bug.
An image in a quiz
Correct Answer: 4
Q3.
What is the temperature shown on the thermometer?
An image in a quiz
Correct Answer: 75, 75 degrees, 75°
Q4.
Match the equation to the factors pairs that would be best used to help solve the calculations.
Correct Answer:50 × 96 = ___,2 and 50

2 and 50

Correct Answer:44 × 25 = ___,4 and 25

4 and 25

Correct Answer:52 × 20 = ___,5 and 20

5 and 20

Q5.
Tick the three factor expression that could be represented by this equation. 64 × 25 = ___
6 × 25 × 4 = ___
6 × (25 × 4) = ___
Correct answer: 16 × (4 × 25) = ___
5 × (2 × 64) = ___
Q6.
Tick the equations that are true.
Correct answer: 20 × 68 × 5 = 68 × 100
Correct answer: 8 × (25 × 4) = 8 × (20 × 5)
Correct answer: 12 × (50 × 2) > 2 × (50 × 12)
20 × 5 × 28 < 100 × 28