Starter quiz
- Which of the following expressions has the same sum as 306 + 30? Can you reason without calculating?
- 300 + 36 ✓
- 310 + 26 ✓
- 305 + 29
- 306 + 32
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- Round 23,654 to the nearest multiple of 10
- '23,650' ✓
- Use an efficient strategy to calculate 56.75 + 22.25 = ______
- '79' ✓
- Use the correct inequality symbol to make this correct: 349,207 ______ 349,086
- '>' ✓
- Use rounding, estimating, comparing or reasoning to determine the missing symbol in this inequality statement. 36 + 23 ______ 23 + 47
- '< ' ✓
- Use an efficient strategy to calculate 10,000 − 8,655 = ______
- '1,345' ✓
Exit quiz
- Select the correct symbol to compare the expressions. 40.36 − 21.63 ___ 39.86 − 27.91
- <
- > ✓
-
- Select the correct symbol to compare the expressions. 12,453 − 6,104 ___ 27,896 − 19,317
- < ✓
- >
-
The unknown subtrahend in the diagram below is ______- '105' ✓
- Use an efficient strategy to calculate the unknown value g in g − 26,100 = 47,865 − 28,300
- '45,665' ✓
- Use an efficient strategy to calculate the unknown value g in 46.5 − 12.6 = 107.9 − g
- '74' ✓
- Izzy begins with 350 g of plasticine and removes 125 g. Jun begins with an unknown mass of plasticine and removes 90 g. Now they have the same mass of plasticine. How much did Jun begin with? ______ g
- '315' ✓
Worksheet
Presentation
Video
Lesson Details
Key learning points
- If the minuend and subtrahend are changed by the same amount, the difference stays the same.
- If you increase or decrease the minuend, the difference increases or decreases by the same amount.
- If you increase the subtrahend then the difference decreases.
- If you decrease the subtrahend then the difference increases.
Common misconception
Pupils immediately calculate expressions instead of considering the relationship between expressions.
Take time to model interrogation of values within expressions, identifying relationships between them. Encourage this reasoning and show how it can be more efficient than calculation especially in situations with larger values.
Keywords
Unknown - An unknown is a quantity that has a set value but it is represented by a symbol or letter.
Equation - An equation is used to show that one number, calculation or expression is equal to another.
Expression - An expression contains one or more values, where each value is separated by an operator.
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