ARMY OF ANTS [DAY 2]
SUBTRACTION STRATEGY: ROUND THE SUBTRAHEND AND ADJUST
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
Purposeful Practice
Resources & Downloads
Educator Discussion Area
Intentionality & Unit Overview
Length of Unit: 5 Days
Access each lesson from this unit using the navigation links below
Be sure to read the teacher guide prior to running the task. When you’re ready to run the task, use the tabs at the top of the page to navigate through the lesson.
Intentionality…
The purpose of the Day 2 activities is to reinforce key concepts from Day 1. 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:
- 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
- Efficient operational sense strategies should be number oriented
- Subtraction can be used in either take away, comparison, or missing addend situations. Take away is explored in this task.
- Subtraction represents the difference or space between two numbers
- Models can be used to connect concrete to abstract
Math Talk
To practice rounding the subtrahend then adjusting, have your students work through these problems one at a time. As you present each problem, provide students with some quiet, individual think 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.
The number strings are created to lead students through the idea of subtracting off the decade number and then connecting to Rounding the Subtrahend and adjusting.
String 1:
27 – 10
37 – 10
45 – 10
String 2:
34 – 20
54 – 20
44 – 30
String 3:
Login/Join to access the entire Teacher Guide, downloadable slide decks and printable handouts for this lesson and all problem based units.
String 4:
Login/Join to access the entire Teacher Guide, downloadable slide decks and printable handouts for this lesson and all problem based units.
Visual Math Talk Prompt #1
Facilitator Note:
We want students to mentally subtract 10 rather than having to track on their fingers. Students may have to track initially but be very explicit about what is happening in the tens column when 10 is removed. Visual Math Talk Prompt #2
Similar to the first prompt, this string is purposefully crafted so that students practice subtracting off the decade and recognize the ease of doing that mentally.
Some students will be able to subtract 30 in one jump. Regardless, students are encouraged to subtract in groups of 10 to eliminate counting back by ones.
Visual Math Talk Prompt #3
Login/Join to access the entire Teacher Guide, downloadable slide decks and printable handouts for this lesson and all problem based units.
Visual Math Talk Prompt #4
Login/Join to access the entire Teacher Guide, downloadable slide decks and printable handouts for this lesson and all problem based units.
Purposeful Practice
Small Group Game
Login/Join to access the entire Teacher Guide, downloadable slide decks and printable handouts for this lesson and all problem based units.
Small Group Assessment Opportunity
Login/Join to access the full teacher guides, downloadable slide decks and printable handouts for this lesson and all problem based units.
Resources & Downloads
Login/Join to access the entire Teacher Guide, downloadable slide decks and printable handouts for this lesson and all problem based units.
Educator Discussion Area
Login/Join to access the entire Teacher Guide, downloadable slide decks and printable handouts for this lesson and all problem based units.
Explore Our 60+ Problem Based Units
This Make Math Moments Lesson was designed to spark curiosity for a multi-day unit of study with built in purposeful practice, number talks and extensions to elicit and emerge strategies and mathematical models.
Dig into our other units of study and view by concept continuum, grade or topic!
