Lesson 6: Rounding Big Numbers

Getting Started

Questions to Explore

  • How does place value work?
  • How can we use place value to name, create, and compare numbers to a million?
  • How do we write and speak in mathematical language?

Skills

  • Read and write multi-digit whole numbers using base-ten numerals, number names, and expanded form
  • Use place value understanding to round multi-digit whole numbers to any place

Materials

  • fine point dry-erase markers (kit)
  • whiteboard (kit)

Introduction

Materials: fine point dry-erase markers (kit), whiteboard (kit)
Provide time for your child to do the problems at the following web link. They provide her practice with rounding to the nearest 10 and 100. If needed, allow her to refer to the "Rounding Round-Up" sheet in her Interactive Notebook.
Web Link
Write 5,632 on the whiteboard, and ask your child to round it to the nearest 10 and 100. (5,630 and 5,600) Now, say, "I wonder what the round number will be if you round this number to the nearest 1,000. Another way to think about this is to picture a number line and to determine whether this number is closer to 5,000 or 6,000." Allow your child to provide an answer. She should note that 5,600 rounds to 6,000. Now, say, "We can round even really big numbers, and we often round big numbers to make our work easier and to communicate when we don't have to be really exact or precise."

Next, give your child the whiteboard and dry-erase markers, and ask her to write the following numbers as you dictate them:
  • 3,489
  • 45,823
  • 595,456
Ask her to round the first number to the nearest thousand. If she uses the method on the "Rounding Round-Up" sheet (from her Interactive Notebook), she would underline the 3 and look at the number to its right (4). Since 4 is less than 5, the underlined number remains the same and the numbers to the right change to zeros (3,000).

Ask her to use the same method to round the second number to the nearest thousand. (46,000) Have her erase and rewrite the number and then round it to the nearest ten thousand (50,000).

Now have her round the third number to the nearest ten thousand. (600,000) This example is a special case. Ask her to explain why this number behaves differently (the 9 rounds to 10, so the 0 goes in the ten thousand place, and the 1 gets added to the hundred thousand place). Another way to think of this is that the number will either round to 500,000 or 600,000, and it is closer to 600,000.

Finally, ask her if this same number can be rounded to the millions place. As needed, explain that even though a digit might not exist in a place (imagine zero there), if the digit to the right of that place is 5 or more, then she can round up to 1 in the place without a digit. Say, "When you look at 595,456, you can ask yourself whether that number is closer to one million or to zero." She should find that the number rounds to 1,000,000.