MA2-5NA: uses mental and written strategies for addition and subtraction involving two-, three-, four- and five-digit numbers
|Students should be encouraged to estimate answers before attempting to solve problems in concrete or symbolic form. There is still a need to emphasise mental computation, even though students can now use a formal written method.|
In Stage 2, it is important that students apply and extend their repertoire of mental strategies for addition and subtraction. The use of concrete materials to model the addition and subtraction of two or more numbers, with and without trading, is intended to provide a foundation for the introduction of the formal algorithm in Addition and Subtraction 2.
|When developing a formal written algorithm, it will be necessary to sequence the examples to cover the range of possibilities, which include questions without trading, questions with trading in one or more places, and questions with one or more zeros in the first number.|
|LANGUAGE||Students should be able to communicate using the following language: plus, add, addition, minus, the difference between, subtract, subtraction, equals, is equal to, empty number line, strategy, digit, estimate, round to, change (noun, in transactions of money).|
Word problems requiring subtraction usually fall into two types:
Take away – How many remain after some are removed?
Comparison – How many more need to be added to a group? What is the difference between two groups?
Students need to be able to translate from these different language contexts into a subtraction calculation.
Apply place value to partition, rearrange and regroup numbers to at least tens of thousands to assist calculations and solve problems(ACMNA073)
|select, use and record a variety of mental strategies to solve addition and subtraction problems, including word problems, with numbers of up to and including five digits, eg 159 + 23: ‘I added 20 to 159 to get 179, then I added 3 more to get 182’, or use an empty number line:|
|– pose simple addition and subtraction problems and apply appropriate strategies to solve them (Communicating, Problem Solving)|
|use a formal written algorithm to record addition and subtraction calculations involving two-, three-, four- and five-digit numbers, eg|
solve problems involving purchases and the calculation of change to the nearest five cents, with and without the use of digital technologies(ACMNA080)
|solve addition and subtraction problems involving money, with and without the use of digital technologies|
|– use a variety of strategies to solve unfamiliar problems involving money (Communicating, Problem Solving)|
|– reflect on their chosen method of solution for a money problem, considering whether it can be improved (Communicating, Reasoning)|
|calculate change and round to the nearest five cents|
|use estimation to check the reasonableness of solutions to addition and subtraction problems, including those involving money|