Overview
This lecture covers how to estimate sums and differences by rounding numbers to a specified place value before performing addition or subtraction.
Estimating Sums and Differences
- Estimating involves rounding numbers to a particular place value (hundreds or thousands) and then adding or subtracting.
- Read instructions carefully to know whether to round to the nearest hundred or thousand.
- For rounding: If the digit after your place value is 5 or higher, round up; if it's 4 or lower, keep the digit the same.
- After rounding, perform the addition or subtraction mentally with the simpler, rounded numbers.
Example Problems
- Example 1: Round 6,287 to the nearest hundred (6,300); round 2,647 to the nearest hundred (2,600); 6,300 + 2,600 = 8,900.
- Example 2: Round numbers to the nearest thousand, then subtract or add as needed.
Practice Problems (Reviewed)
- Problem 1: 5,000 + 2,000 = 7,000 (rounding each to the nearest thousand).
- Problem 2: 12,000 - 9,000 = 3,000 (rounding each to the nearest thousand).
- Problem 3: 77,000 + 12,000 = 89,000 (rounding each to the nearest thousand).
Upcoming Class Problems
- Round each number to the nearest hundred:
- 197 + 653
- 3,456 + 4,321
- 8,649 - 5,718
Key Terms & Definitions
- Estimate — Finding an approximate answer by rounding numbers before calculating.
- Rounding — Adjusting a number to a specified place value based on the digit that follows.
- Sum — The result of addition.
- Difference — The result of subtraction.
Action Items / Next Steps
- Complete the three class problems by rounding each number to the nearest hundred and then adding or subtracting as instructed.
- Double check whether each problem requires addition or subtraction.
- Review rounding rules if needed before next class.