Rich tasks
- This is an open-ended activity that requires students to work in teams and create a presentation showing how tidy numbers can be used to solve addition or subtraction problems. The task can be done as the students gain enough knowledge to complete it, or towards the end of the chapter to review strategies that have been learned.
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1. Sharks and seals
- This activity will work well with students working in groups.
- It may be helpful to create some roles for group members so that students work collaboratively (for example, leader, reader, writer, time-keeper, etc.) and to ensure that materials or resources that might be useful are readily accessible.
- Teachers might also like to provide some structure for the task, for example working through problem solving steps.
This video with four steps set to catchy music might be helpful too: https://www.youtube.com/watch?v=GLsg2iGMpI4
- Depending on the time available for presenting, teachers may select (or suggest students choose):
- the order in which each group does the problems
- which problem(s) each group will share if presenting to the whole class, or which groups will share together if sharing with another group. Students will probably benefit most if each problem is presented by at least one group sharing a variety of different strategies.
Subtracting by jumping back through a tens number page 64
- Identify a fact that can be partitioned to jump back through a tens number.
- Understand why this is an efficient strategy for mental calculations and explore how the strategy can be recorded.
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Teacher notes
- Students need to understand that partitioning the number being subtracted (the subtrahend) so that the first jump is to a tens number is important. For example, 13 – 5 = ? will always involve the 5 being split into 3 + 2. Choosing the fact which makes this possible is what makes this strategy efficient. Using place value materials, such as tens frames, will help students see that while other facts also make 5, they do not make solving the equation quicker or easier.
Adding using tens numbers page 67
- For jumping through a tens number, identify the fact that will take them to the next tens number first.
- For adding by making a tidy number (on page 70), identify what needs to be subtracted from one addend, and added to the other, in order to make a tens number.
- Understand that for both strategies, an efficient strategy makes finding the answer quicker and easier.
- Explore ways of recording both strategies.
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Teacher notes
- Students often find subtraction through a tens number easier than addition since the most efficient way to partition always involves subtracting the number in the ones place and then the balance of the number. When adding there may be more than one efficient way to partition a number.
- Listing possible ways to partition the numbers being added and discussing which is most helpful, provides meaningful opportunities for students to revise facts to ten if they have not mastered them.
- Using place value materials helps students see what is needed to make a ten, and a number line supports students’ understanding of the most efficient way to partition the number being added in order to reach the next ten.
