# Flexible additive strategies - 2 digit numbers

This resource has been developed in partnership with the NSW Mathematics Strategy Professional Learning team, Curriculum Early Years and Primary Learners, and Literacy and Numeracy.

## Using the resource

This resource is the second section of a four-part resource supporting additive thinking. Use this resource in conjunction with the other resources in this series in order to support a connected network of critical mathematical concepts, skills and understanding.

### Task 1: Let’s talk 1

Students view the ‘Let’s talk 1' video.

Students roll three dice and use addition and subtraction to match them to a set of numeral cards 0-27.

• Variation 1: Play in larger teams

• Variation 2: ‘Freeze’ the game between two players at a particular moment and involving the class in an investigation about what move to make next and what may happen as a result

• Variation 3: Introduce a ‘free pass’ card

### Task 3: Subtraction face off

Students use playing cards to form a 2-digit number and a 1-digit number then arrange the cards to make the smallest difference.

Students form small groups and use playing cards to form a 2-digit numbers The aim is to get 2 numbers with a difference of 45, or, at the end of 5 turns each, the student with a difference closest to 45.

• Variation 1: Use a hundred chart to assist mental calculations

• Variation 2: After creating the first two digit number, ask questions such as ‘What numbers would or wouldn’t like to draw next and why?

• Variation 3: Change the challenge to addition of two 2-digit numbers with the goal of being as close as possible to 100. Encourage students to use their knowledge of part-whole to ten to work out solutions

### Task 5: Strategic part-part-whole thinking

Students investigate different ways to partition numbers

• Variation 1: Change the target number

### Task 6: How might we?

Students use pencils to practice different grouping strategies

• Variation 1: Plan for a class party and determine how many packets of 10 items (such as cups, spoons) would be needed for the class, discussing how many would be left over.

Students roll 2 large 1 – 10 dice record their results on an 11 x 11 addition and subtraction grid.

### Task 8: How can we represent that?

Students work out as many ways as possible to solve the problem 23 + 38

• Variation 1: Change the numbers used in the problem in order to examine the efficiency of different strategies

• Variation 2: Students to model all possible strategies they can think of and reflect upon the efficiency of each