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Subject

Math, Science & Technology

Objectives

Students will be able to:

• Recognize when regrouping is needed within a subtraction problem.
• Compose and decompose a unit of higher value.
• Evaluate subtraction expressions that involve regrouping.

Description

This lesson is an introduction to subtracting mixed numbers. The objective of this lesson is to teach students the concept of decomposing with whole numbers in order to transition into decomposing mixed numbers for subtraction.

Website(s)

National Library of Virtual Manipulatives

Duration

Approximately 45 minutes, one class period

Materials/Web Resources

• SMART Board (if available), laptop, projector, SMART Notebook software
• Internet access, website: Virtual Manipulatives
• Teacher-made worksheet with five subtraction problems that involve regrouping (see attached)
• Teacher-made table for regrouping

Procedure

• Do Now: Give the students a word problem that involves subtraction with regrouping.
  Example: Nick and Keith are going apple picking. Apples cost $3.99 per bag. Nick picks five bags of apples and Keith picks two bags of apples. How much more did Nick spend? Use this word problem to asses student’s prior knowledge of subtraction with regrouping.
• Discussion: What do you know about regrouping? Record student ideas and develop a class list. The teacher will record student comments on SMART Board using stylus (or on a white/chalk board if SMART Board is not available).
• Discuss composing and decomposing and develop a class definition. Composing-make up. Decomposing-break down.
• Bring up Virtual Manipulatives website. Prior to evaluating the expressions on the website, ask the students, "Do you need to decompose? Why or why not?"
• Have students come up to SMART Board (or shared computer) to use virtual manipulatives. They will solve the subtraction problems on the website.
• Complete regrouping tables a class. Students will come to the SMART Board (white/chalk board) and use the stylus to complete the table.

Assessment

• Students will analyze expressions and decide if expressions require regrouping or not (regrouping table). Teacher will check that students can recognize when regrouping is needed with 80% accuracy.
• Students will decompose units of higher value in order to evaluate subtraction expressions (subtracting with regrouping practice).
• Homework Assignment: Students will evaluate 5 expressions that involve subtraction with regrouping (worksheet). Teacher will collect and check for 80% accuracy.

Support Materials

The following documents are used in the execution of this lesson plan.

subtraction.pdf

subtraction.xbk

worksheets and answer keys

SMART Board

This instructional content was intended for use with a SMART Board.

Author

Brandi Lange, Enlarged City School District of Middletown

Related Academic Standards

New York State

MST3.6.PS.13 Students model problems with pictures/diagrams or physical objects.

MST3.6.CM.4 Students share organized mathematical ideas through the manipulation of objects, numerical tables, drawings, pictures, charts, graphs, tables, diagrams, models, and symbols in written and verbal form.

MST3.6.R.1 Students use physical objects, drawings, charts, tables, graphs, symbols, equations, or objects created using technology as representations.