Solving Result Unknown Problems with Three-digit Numbers.

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Objective

SWBAT solve result unknown problems with three-digit numbers.

Big Idea

Students identify, practice, and share strategies for solving result unknown problems that use three-digit numbers.

Lesson Author

Caitlin Vaughan

Grade Level

Second grade

Subjects

Math

Number Sense and Operations

Standards

2.NBT.B.7

Add and subtract within 1000, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method. Understand that in adding or subtracting three-digit numbers, one adds or subtracts hundreds and hundreds, tens and tens, ones and ones; and sometimes it is necessary to compose or decompose tens or hundreds.

2.NBT.B.9

Explain why addition and subtraction strategies work, using place value and the properties of operations. (Explanations may be supported by drawings or objects.)

MP2

Reason abstractly and quantitatively.

Introduction/Hook

10 minutes

Activating Prior Knowledge with Entrance Tickets

I start class by handing out an entrance ticket. I allow students 5-7 minutes to work on the entrance ticket. This entrance ticket assesses students' understanding of adding four three-digit numbers (a skill that we introduced yesterday). We will use the results of this entrance ticket during the introduction to new material.

Entrance ticket:

The donut shop has 142 chocolate donuts, 320 sprinkle donuts, 115 glazed donuts, and 400 pumpkin donuts. How many donuts does the donut shop have in all?

When finished with the entrance ticket, have at least one student share his/her response and how he/she solved the problem.

Introduction to New Material

10 minutes

Now, let’s say that everyone who came to the donut shop bought sprinkle donuts and they sold out. How many donuts does the donut shop have now?

Turn and talk: What should I do to solve this problem?

Students might suggest using the total and subtracting 320 from it. Others might suggest adding up the chocolate, glazed, and pumpkin donuts and leaving the sprinkle donuts out to determine the total. For each strategy suggestion, I have a student model his/her thinking or as the student talks, I model the strategy on the board. Write the students' strategies on the board or on an anchor chart for student reference.

Now that we’ve talked about strategies for solving a problem like this, please turn your entrance ticket over and solve this problem on the back.

As students work, circulate to see (1) which strategy they are using and (2) What common mistakes students are making.

After students have finished, have one or two students share their work. Also use this time to correct any potential mistakes or misunderstandings students have.

Guided Practice

10 minutes

Now I am going to give you a chance to work with a partner and solve a problem similar to the one we worked on as a team.

I have students work in heterogeneous partners so that they can support each other in solving the problem. I give each pair two worksheets and allow students to work for about 5-10 minutes on the problem.

When finished, I bring the class back together, and go over the problem, stopping to discuss various strategies and (of course) add them to the strategy chart.

Weekly Quiz/ Friday Skills Assessment

20 minutes

Today we have practiced a new skill--solving result unknown word problems with three-digit numbers! We are now going to to show what we know on our Friday Skills Assessment.

I hand out the Friday Skills Assessment (weekly quiz) and allow students to work independently.

I use data from this assessment to determine which concepts I need to re-teach during my morning math meeting.

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