Lesson 46: Rounding Decimals

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Lesson Objectives

• Round decimals to the nearest whole number, tenth, or hundredth.
• Apply rounding rules: round up if next digit ≥ 5, round down if < 5.
• Use rounding to simplify calculations and estimate results.
• Check answers for reasonableness using rounding.

Introduction

Rounding decimals helps simplify numbers and makes calculations easier. It is especially useful for estimation and checking answers in real-world problems.

Examples

Round to the nearest whole number

4.6 → 5, 7.2 → 7

Round to the nearest tenth

3.76 → 3.8, 5.43 → 5.4

Round to the nearest hundredth

2.678 → 2.68, 9.432 → 9.43

Practice Problems

1. Round 6.487 to the nearest whole number, tenth, and hundredth.
2. Round 3.249 to the nearest tenth.
3. Round 8.765 to the nearest whole number.
4. Check the reasonableness of 4.68 × 3.2 ≈ 15 using rounding.

Summary

Rounding decimals makes numbers easier to work with and helps verify calculations. Always follow the rule: if the next digit is 5 or greater, round up; otherwise, round down. Use rounding to estimate answers quickly and accurately.