# YEAR 3 MATHS FOCUS

## NUMBERS AND ALGEBRA

Addition & Subtraction

Learning Experiences

Addition & Subtraction

## ADDITION & SUBTRACTION

OUTCOME

A student:

MA2-5NA: uses mental and written strategies for addition and subtraction involving two-, three-, four- and five-digit numbers

Teaching Points | Students need to understand the different uses for the = sign, eg 4 + 1 = 5, where the = sign indicates that the right side of the number sentence contains ‘the answer’ and should be read to mean ‘equals’, compared to a statement of equality such as 4 + 1 = 3 + 2, where the = sign should be read to mean ‘is the same as’. |

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. | |

One-cent and two-cent coins were withdrawn by the Australian Government in 1990. Prices can still be expressed in one-cent increments, but the final bill is rounded to the nearest five cents (except for electronic transactions), eg $5.36, $5.37 round to $5.35 $5.38, $5.39, $5.41, $5.42 round to $5.40 $5.43, $5.44 round to $5.45. |

Language | Students should be able to communicate using the following language: plus, add, addition, minus, the difference between, subtract, subtraction, equals, is equal to, is the same as, number sentence, empty number line, strategy, digit, estimate, round to. |

## Expectations of Attainment

Recall addition facts for single-digit numbers and related subtraction facts to develop increasingly efficient mental strategies for computation(ACMNA055) | add three or more single-digit numbers |

model and apply the associative property of addition to aid mental computation, eg 2 + 3 + 8 = 2 + 8 + 3 = 10 + 3 = 13 | |

apply known single-digit addition and subtraction facts to mental strategies for addition and subtraction of two-, three- and four-digit numbers, including: the jump strategy on an empty number line, eg 823 + 56: 823 + 50 = 873, 873 + 6 = 879 the split strategy, eg 23 + 35: 20 + 30 + 3 + 5 = 58 the compensation strategy, eg 63 + 29: 63 + 30 = 93, subtract 1 to obtain 92 using patterns to extend number facts, eg 500 – 200: 5 – 2 = 3, so 500 – 200 = 300 bridging the decades, eg 34 + 26: 34 + 6 = 40, 40 + 20 = 60 changing the order of addends to form multiples of 10, eg 16 + 8 + 4: add 16 to 4 first using place value to partition numbers, eg 2500 + 670: 2500 + 600 + 70 = 3170 partitioning numbers in non-standard forms, eg 500 + 670: 670 = 500 + 170, so 500 + 670 = 500 + 500 + 170, which is 1000 + 170 = 1170 | |

– choose and apply efficient strategies for addition and subtraction (Problem Solving) | |

– discuss and compare different methods of addition and subtraction (Communicating) | |

use concrete materials to model the addition and subtraction of two or more numbers, with and without trading, and record the method used | |

select, use and record a variety of mental strategies to solve addition and subtraction problems, including word problems, with numbers of up to four digits | |

– give a reasonable estimate for a problem, explain how the estimate was obtained, and check the solution (Communicating, Reasoning) | |

use the equals sign to record equivalent number sentences involving addition and subtraction and so to mean ‘is the same as’, rather than to mean to perform an operation, eg 32 – 13 = 30 – 11 | |

– check given number sentences to determine if they are true or false and explain why, eg ‘Is 39 – 12 = 15 + 11 true? Why or why not?’ (Communicating, Reasoning) |

Recognise and explain the connection between addition and subtraction (ACMNA054) | demonstrate how addition and subtraction are inverse operations |

explain and check solutions to problems, including by using the inverse operation |

Represent money values in multiple ways and count the change required for simple transactions to the nearest five cents (ACMNA059) | calculate equivalent amounts of money using different denominations, eg 70 cents can be made up of three 20-cent coins and a 10-cent coin, or two 20-cent coins and three 10-cent coins, etc |

perform simple calculations with money, including finding change, and round to the nearest five cents | |

calculate mentally to give change |

Learning Experiences

To be added