Rounding Decimals

What You’ll Learn

In this lesson you’ll learn the rules for rounding decimals to different places and how to apply them for quick estimates.

The Concept

Rounding decimals simplifies numbers while keeping them close to the original value. Look at the digit to the right of the place you’re rounding to:

• 5 or higher → round up
• Less than 5 → round down (keep the digit the same)

Examples:

• Round $3.78$ to nearest tenth: Look at hundredths (8 ≥ 5) → $3.8$
• Round $3.78$ to nearest whole: Look at tenths (7 ≥ 5) → $4$
• Round $12.345$ to nearest hundredth: Look at thousandths (5 ≥ 5) → $12.35$

Trailing zeros after rounding can be dropped ($12.350$ becomes $12.35$).

Worked Examples

Round $7.649$ to:

1. Nearest tenth: Look at hundredths (4 < 5) → $7.6$
2. Nearest hundredth: Look at thousandths (9 ≥ 5) → $7.65$
3. Nearest whole: Look at tenths (6 ≥ 5) → $8$

Real-World Applications

Rounding decimals is used for estimates: gas at 3.789 per gallon rounded to 3.79; tip calculation (18.5% of a 42 dollar meal ≈ 8 dollars); or measurements (cut wood to 5.73 feet rounded to 5.7 feet). It helps make quick decisions without exact precision.

You’ve Got This

Rounding is just deciding whether to keep or bump up based on the next digit, like approximating how much something costs. Practice on receipts or prices, and always ask “is it closer to this or that?” You’ll get accurate estimates in no time.

Quiz

Round 4.673 to the nearest tenth.

• A.4.7
• B.4.6
• C.5.0
• D.4.67

Round 9.248 to the nearest hundredth.

• A.9.25
• B.9.24
• C.9.20
• D.9.30

A bill is 67.89 dollars. Rounded to the nearest dollar, how much?

• A.68 dollars
• B.67 dollars
• C.70 dollars
• D.67.90 dollars

Round 12.3456 to the nearest thousandth.

• A.12.346
• B.12.345
• C.12.350
• D.12.300

Round 0.9951 to the nearest tenth.

• A.1.0
• B.0.9
• C.0.99
• D.0.10