AVID READER [DAY 4]
SUBTRACTION STRATEGY: ADD UP INSTEAD
Explore efficient strategies to subtract values within 50
Intentionality
Math Talk
Visual Math Talk Prompt #1
Visual Math Talk Prompt #2
Visual Math Talk Prompt #3
Visual Math Talk Prompt #4
Visual Math Talk Prompt #5
Visual Math Talk Prompt #6
Purposeful Practice
Resources & Downloads
Educator Discussion Area
Intentionality & Unit Overview
Length of Unit: 5 Days
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Students will deepen their understanding of difference in relation to subtraction. The numbers have been specifically chosen to elicit the Think Addition subtraction strategy.
Intentionality…
The purpose of the Day 4 activities is to reinforce key concepts from Day 3. Students will engage in a string of related problems through a math talk and will have an opportunity to complete purposeful practice. The math talk and purposeful practice serve to develop a deeper understanding of the following big ideas.
Some of the big ideas that may emerge through this task include:
- Understanding hierarchical inclusion allows for flexible composing and decomposing of numbers
- Numbers can be decomposed by separating a whole into two or more parts
- Subtraction names the missing part in terms of the whole
- Different subtraction situations will elicit different strategies
- Number relationships provide the foundation for strategies to help students remember basic facts
- Subtraction can be used in either take away, comparison, or missing addend situations.
- Models can be used to connect concrete to abstract
Before starting this unit, students should be familiar with:
- Facts of 10 ( e.g., 6 + 4 = 10, 10 – 4 = 6)
- Flexibility when decomposing numbers (e.g., 13 can be decomposed into 10 and 3, but also 9 and 4, 8 and 5, etc)
Math Talk
To deepen the understanding of subtraction as the difference between two numbers, have your students work through these problems one at a time. As you present each problem, provide students with some quiet, individual thought time during which they can solve the problem and show their thinking on a dry erase board, paper, etc. Then have students share their thinking either in pairs or with the whole group. As you facilitate these conversations, emphasize that the Think Addition strategy is efficient because the numbers are close together. The numbers in the math talk are purposefully chosen to highlight this.
The problems are supporting the move towards subtracting numbers mentally and creating number sense. Students should be encouraged to do parts of the subtracting in their head. For this purpose students need to develop a mental number line. The mental number line will be an asset from students for many different strategies. It will take exposure and opportunities with the number line to develop this, but it will be time well spent. For this purpose, open number lines are used in the visual prompts.
String 1:
50 – 47
50 – 43
50 – 38
String 2:
40 – 35
40 – 29
41 – 36
String 3:
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Prompt 4:
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Prompt 5:
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Prompt 6:
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Visual Math Talk Prompt #1
Facilitator Note:
Facilitator’s Note: The numbers in these prompts are fairly close together and therefore it is more efficient to use the Think Addition strategy. Students may still use a Take Away strategy but during the discussion of the prompts highlight the ease for adding up from the subtrahend.
There are no visuals for the first 2 prompts to encourage students to apply their understanding from the previous days. The last prompt is animated with an open number line to make a connection to Think Addition strategy highlighted throughout this unit.
The open number line (or empty number line) is an incredible tool for students to use to demonstrate their thinking. It allows flexibility from the traditional number line because students do not have to count the “ticks’ or “spaces”, instead they may jot their thinking anywhere on the line. Visual Math Talk Prompt #2
Facilitator’s Note: The first two prompts are related to the facts of 10 then the last prompt is slightly above the decade (41).
During discussion of the last prompt, encourage students to recognize the connection to “getting to the decade” then just adding one more. It is easier to add on from a decade number. This count may also have been tracked on fingers since it is small (5). Visual Math Talk Prompt #3
Visual Math Talk Prompt #4
Visual Math Talk Prompt #5
Visual Math Talk Prompt #6
Purposeful Practice
Small Group Game
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Small Group Assessment Opportunity
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Resources & Downloads
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Educator Discussion Area
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