Curriculum  /  Math  /  3rd Grade  /  Unit 1: Rounding, Addition, and Subtraction  /  Lesson 10

Rounding, Addition, and Subtraction

Lesson 10

Math

Unit 1

3rd Grade

Lesson 10 of 14

Objective

Solve one-step word problems involving addition, using rounding to assess the reasonableness of answers.

Common Core Standards

Core Standards

  • 3.NBT.A.1 — Use place value understanding to round whole numbers to the nearest 10 or 100.
  • 3.NBT.A.2 — Fluently add and subtract within 1000 using strategies and algorithms based on place value, properties of operations, and/or the relationship between addition and subtraction.
  • 3.OA.D.8 — Solve two-step word problems using the four operations. Represent these problems using equations with a letter standing for the unknown quantity. Assess the reasonableness of answers using mental computation and estimation strategies including rounding. This standard is limited to problems posed with whole numbers and having whole-number answers; students should know how to perform operations in the conventional order when there are no parentheses to specify a particular order (Order of Operations).

Foundational Standards

  • 2.NBT.B.7
  • 2.OA.A.1

Criteria for Success

  1. Solve one-step word problems involving addition (MP.4).
  2. Use rounding to estimate the answer to a subtraction problem in each of the following cases: 
    1. Use rounding to assess the reasonableness of one’s own or someone else’s answer (MP.1). 
    2. Use rounding when an exact answer is not needed or expected (e.g., the problem says "about" or "approximately").
  3. Determine which estimate is closest to the actual solution and understand why it’s closest. 
  4. Understand the effect rounding has on a solution and why (i.e., why one’s estimate is higher or lower than the actual solution).

Tips for Teachers

  • Students should be familiar with all addition and subtraction situation types from Grade 2. Thus, the focus of the lesson should be on the key advancement – assessing the reasonableness of their answers to these contextual problems.
  • If students struggle with interpreting any of these problems, remind students of tape diagrams as a way to represent a problem, which they should be familiar with from Grades 1 and 2.
  • Students may struggle with seeing the usefulness of rounding to assess reasonableness in this and even subsequent lessons, especially since "rounding two numbers before computing can take as long as just computing their sum or difference" (NBT Progression, p. 12). To continue to reinforce its importance, find opportunities to use a mistake as a learning opportunity for how rounding to assess reasonableness can help to identify these mistakes.
  • This lesson provides an opportunity to connect two domains in the grade, 3.OA and 3.NBT, since students will be solving word problems involving addition. While students will not solve two-step problems involving addition and/or subtraction (3.OA.8) until Lesson 14, they will use rounding to assess reasonableness of their answers to one-step problems that requires addition within 1,000 in this lesson, connecting standards 3.OA.8, 3.NBT.1, and 3.NBT.2.
Fishtank Plus

Unlock features to optimize your prep time, plan engaging lessons, and monitor student progress.

Anchor Tasks

25-30 minutes

Problem 1

Mr. Silver went back-to-school shopping for school supplies. Here is what he wants to buy:

He has $550 to spend and wants to make sure he has enough money to buy everything. But, he doesn't have a pen and paper to figure out the cost.

a.   Do you think Mr. Silver has enough money? Try not to use pen and paper to help him figure it out!

b.   Check whether Mr. Silver has enough money. You may use paper and pencil for this step. 

Guiding Questions

Create a free account or sign in to access the Guiding Questions for this Anchor Problem.

Student Response

Upgrade to Fishtank Plus to view Sample Response.

Problem 2

Luke and Josh collect baseball cards. Luke has 347 baseball cards. Luke has 34 fewer baseball cards than Josh. How many baseball cards does Josh have? Solve. Then assess the reasonableness of your answer.

Guiding Questions

Create a free account or sign in to access the Guiding Questions for this Anchor Problem.

Student Response

Upgrade to Fishtank Plus to view Sample Response.

References

EngageNY Mathematics Grade 3 Mathematics > Module 2 > Topic D > Lesson 17 — Application Problem

Grade 3 Mathematics > Module 2 > Topic D > Lesson 17 of the New York State Common Core Mathematics Curriculum from EngageNY and Great Minds. © 2015 Great Minds. Licensed by EngageNY of the New York State Education Department under the CC BY-NC-SA 3.0 US license. Accessed Dec. 2, 2016, 5:15 p.m..

Modified by Fishtank Learning, Inc.

Problem 3

Sadie, Rachel, and Kahlid each spent time reading over the summer. Sadie read 119 pages, Rachel read 247 pages, and Kahlid read 332 pages. They are trying to figure out about how many pages they read altogether. Here’s how each of them computed:

Student Computation
Sadie 100 + 200 + 300
Rachel 110 + 240 + 330
Kahlid 120 + 250 + 330

Whose estimate is closest to the actual solution? How do you know?

Guiding Questions

Create a free account or sign in to access the Guiding Questions for this Anchor Problem.

Student Response

Upgrade to Fishtank Plus to view Sample Response.

Problem Set

15-20 minutes

Discussion of Problem Set

  • In #1(a) how did you round? Compare your method with your partner’s. Which was closer to the actual answer? Why?
  • In #2, how close was your rounded sum to the actual sum? 
  • How does estimating help you check if your answer is reasonable?

Target Task

5-10 minutes

Demarcus gardens for 225 minutes on Saturday. He gardens for 195 minutes on Sunday.

a.   Estimate the total amount of time Demarcus gardens.

b.   How much time did Demarcus actually spend gardening?

Student Response

Upgrade to Fishtank Plus to view Sample Response.

Additional Practice

The Extra Practice Problems can be used as additional practice for homework, during an intervention block, etc. Daily Word Problems and Fluency Activities are aligned to the content of the unit but not necessarily to the lesson objective, therefore feel free to use them anytime during your school day.

Word Problems and Fluency Activities

Word Problems and Fluency Activities

Help students strengthen their application and fluency skills with daily word problem practice and content-aligned fluency activities.

Next

Subtract numbers with up to one decomposition within 1,000.

Lesson 11
icon/arrow/right/large

Lesson Map

A7CB09C2-D12F-4F55-80DB-37298FF0A765

Topic A: Foundations of Place Value

Topic B: Rounding to the Nearest Ten and Hundred

Topic C: Addition and Subtraction Within 1,000

Request a Demo

See all of the features of Fishtank in action and begin the conversation about adoption.

Learn more about Fishtank Learning School Adoption.

Contact Information

School Information

What courses are you interested in?

ELA

Math

Are you interested in onboarding professional learning for your teachers and instructional leaders?

Yes

No

Any other information you would like to provide about your school?

We Handle Materials So You Can Focus on Students

We Handle Materials So You Can Focus on Students

We've got you covered with rigorous, relevant, and adaptable math lesson plans for free