# Lesson 2: Reviewing Rounding to 10 and 100

## Getting Started

### Questions to Explore

• What is rounding and when do we use it?
• How do we write and speak in mathematical language?

### Facts and Definitions

• Rounding: the process of making a number simpler to work with but keeping its value close to the original number

### Skills

• Use place value understanding to round multi-digit whole numbers to any place
• Apply rounding to telling time

### Materials

• fine point dry-erase markers (kit)
• geared clock (kit)
• Interactive Notebook
• whiteboard (kit)

### Introduction

Materials: fine point dry-erase markers (kit), whiteboard (kit)
Write 359+132 and 360+130 on the whiteboard, and ask, "Which of the problems can you figure out more quickly in your head and why?" Your child should note that the second problem is easier because the numbers are easier to work with and there's no carrying involved. Now, ask, "Will the answer to 360+130 be pretty close to the answer to 359+132?" and "Why is that?" Your child should see that the numbers are close to one another and have been changed only a little bit.

At this point, your child may say that the first numbers have been rounded to the nearest 10. If she doesn't mention this, remind her that rounding is the process of making a number simpler to work with but keeping its value close to the original number. Say, "Here, I've rounded the numbers in 359+132 to the nearest 10 to make this addition problem easier for me. This is a great way to check whether my math is correct when I add the original numbers." Provide time for your child to find and compare the sums on the whiteboard. (491 and 490)