Estimate the sum and difference of two 5- to 6-digit numbers by rounding the addends to the nearest large place value of the numbers.

Estimate the Sum and Difference of Two 5- to 6-Digit Numbers

Discussion: Estimating Sum and Difference by Rounding

In this lesson, we will learn how to estimate the sum and difference of two 5- to 6-digit numbers by rounding the numbers to the nearest large place value (e.g., nearest ten thousand, hundred thousand, etc.).

Example 1: Estimate the sum of 345,678 and 876,543 by rounding both numbers to the nearest hundred thousand.

• 345,678 rounded to the nearest hundred thousand is 300,000.
• 876,543 rounded to the nearest hundred thousand is 900,000.
• Estimated sum: 300,000 + 900,000 = 1,200,000.

Example 2: Estimate the difference between 987,654 and 234,567 by rounding both numbers to the nearest hundred thousand.

• 987,654 rounded to the nearest hundred thousand is 1,000,000.
• 234,567 rounded to the nearest hundred thousand is 200,000.
• Estimated difference: 1,000,000 - 200,000 = 800,000.

Steps for Estimating:

• Identify the place value to which you need to round the numbers (e.g., nearest ten thousand, hundred thousand).
• Round each number to that place value.
• Perform the addition or subtraction using the rounded numbers.

Introduction to Estimation

Now that you understand how to estimate the sum and difference, let’s test your skills with a quiz!

Quiz Questions

Your Score

Answer Key