Lesson 17 Round and Round Again

  • Let’s look for patterns in rounding.

Warm-up Number Talk: More Groups, Fewer Groups

Find the value of each expression mentally.

Activity 1 All the Numbers

If you finish early, find the numbers that would round to 100 and to 500 if you’re rounding to the nearest hundred. Compare your lists with a partner’s lists and discuss patterns you see.

  1. What are all the numbers that would round to 50 if you’re rounding to the nearest ten? You can use this number line if it helps you.

    Number line. Scale 30 to 60 by 10's.

  2. What are all the numbers that would round to 70 if you’re rounding to the nearest ten?

  3. What are all the numbers that would round to 600 if you’re rounding to the nearest hundred?

Activity 2 What’s My Mystery Number?

Write down a number between 100 and 1,000 on your index card. This is your mystery number.

Fold your index card in half so that no one can see your mystery number. ​​​​

Can you guess the mystery number?

Write down 3 clues about your mystery number by finishing these sentences:

  1. My mystery number is (odd or even) .

  2. My mystery number rounds to .

  3. My mystery number is between and .

Play What’s My Number?

  1. Read the clues for your mystery number.

  2. Starting with the person on your right, have every member in your team try to guess your mystery number and explain their reasoning.

  3. If they haven’t guessed the mystery number by the time the last person shares, reveal the mystery number.

  4. Repeat steps 1 through 3 with the next person in the group reading the clues for their mystery number.

Practice Problems

Problem 1

  1. What are all the numbers that round to 350 when rounded to the nearest 10?

  2. Which numbers round to 350 when rounded to the nearest ten and round to 400 when rounded to the nearest hundred?

Problem 2

Jada rounds 145 to the nearest ten and gets 150. Then she rounds 150 to the nearest hundred and gets 200. Jada says 145 rounded to the nearest hundred is 200. Do you agree with Jada? Explain or show your reasoning.