New
New
Year 6

Solve subtraction calculations mentally by using known facts

I can solve subtraction calculations mentally by using known facts

New
New
Year 6

Solve subtraction calculations mentally by using known facts

I can solve subtraction calculations mentally by using known facts

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Lesson details

Key learning points

  1. Compensation can be used to simplify subtraction calculations.
  2. Equivalence can be used to simplify subtraction calculations.
  3. A number line can be used to represent compensation and equivalence.

Keywords

  • Minuend - The minuend is the number being subtracted from.

  • Subtrahend - A subtrahend is a number subtracted from another.

  • Partition - Partition is the act of splitting an object or value down into smaller parts.

  • Adjust - When you adjust you make a change to a number. This is done to make a calculation easier to solve mentally.

Common misconception

Known facts in this lesson include complements and two-digit subtractions which some children may find challenging to recall fluently.

It's a good idea, if possible, to do some pre-teaching here to develop the confidence of the children who might find the known facts aspect provides extra cognitive load. Supplying scaffolds such as key bonds to 20 and 100 may also benefit.

For children who find it challenging to recall addition facts fluently, have a list of complements to 100 available to refer to. They might even find a hundred square useful.
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).

Lesson video

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6 Questions

Q1.
In the following equation, which number is the subtrahend? 21 − 4 =17
21
Correct answer: 4
7
Q2.
Solve the following calculation mentally by adjusting the minuend and subtrahend. 76 − 22 =
Correct Answer: 54
Q3.
Solve the following calculation using a mental strategy. = 150 − 68
Correct Answer: 82
Q4.
Solve the following calculation mentally by adjusting the subtrahend and then the difference. 165 − 27 =
Correct Answer: 138
Q5.
Solve the following calculation using a mental strategy. = 4,050 − 98
Correct Answer: 3,952
Q6.
Select the equivalent expressions (equal value) from the list below.
Correct answer: 105 − 56
Correct answer: 254 − 205
300 − 156
85 − 34

6 Questions

Q1.
Use a known fact to find the missing number in this subtraction equation. 46 − 0.35 =
Correct Answer: 45.65
Q2.
Use a mental strategy. = 223 − 0.57
Correct Answer: 222.43
Q3.
Use a mental strategy. 27.43 − 0.22 =
Correct Answer: 27.21
Q4.
Use a mental strategy. = 274.86 − 0.54
Correct Answer: 274.32
Q5.
Use a mental strategy. 1,367,000 − 17,000 =
Correct Answer: 1,350,000
Q6.
Use a mental strategy. 9,284,000 − 22,000 =
Correct Answer: 9,262,000