Training Decimals Rounding Decimals and Estimation
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Rounding Decimals and Estimation

18 min Decimals

Rounding Decimals

Rounding decimals works exactly like rounding whole numbers — look one place to the right of the digit you want to keep and decide whether to round up or stay. The difference is that you may be rounding to the nearest tenth, hundredth, or thousandth instead of the nearest ten or hundred.

Estimation with decimals is a powerful real-world skill. Rounding each number in a calculation to a convenient value lets you quickly check whether your exact answer is in the right ballpark.

Rounding Rule
  1. Find the rounding-place digit.
  2. Look at the digit to its right (test digit).
  3. $\ge 5$: round up. $< 5$: keep.
  4. Drop all digits after the rounding place.
Example 1

Round $3.7461$ to the nearest hundredth.

Hundredths: 4. Test: 6 ($\ge 5$). Round up → $3.75$.

Example 2

Round $0.8534$ to the nearest tenth.

Tenths: 8. Test: 5 ($\ge 5$). Round up → $0.9$.

Example 3

Round $6.997$ to the nearest hundredth.

Hundredths: 9. Test: 7 ($\ge 5$). $9 + 1 = 10$ → carry. Answer: $7.00$.

Estimation

Example 4

Estimate $4.82 \times 3.19$.

$5 \times 3 = 15$. Exact: $15.38$. ✓

Example 5

Estimate $\dfrac{49.7}{5.1}$.

$\approx \dfrac{50}{5} = 10$. Exact: $9.75$. ✓

Practice Problems

1. Round $7.836$ to nearest tenth.
2. Round $0.4951$ to nearest hundredth.
3. Round $12.995$ to nearest hundredth.
4. Round $3.0045$ to nearest thousandth.
5. Estimate $8.73 + 2.18$.
6. Round $0.0672$ to nearest hundredth.
7. Estimate $6.9 \times 4.1$.
8. Round $99.999$ to nearest tenth.
9. Estimate $\$18.45 + \$32.78 + \$9.15$.
10. Round $2.5555$ to nearest thousandth.
11. Estimate $150.4 \div 7.8$.
12. Round $0.0098$ to nearest thousandth.
13. Item costs $\$3.474$. Round to the nearest cent.
14. Estimate $3.97 \times 2.04 \times 5.1$.
15. Round $45.4545$ to nearest tenth.
Show Answer Key

1. $7.8$

2. $0.50$

3. $13.00$

4. $3.005$

5. $\approx 11$

6. $0.07$

7. $\approx 28$

8. $100.0$

9. $\approx \$60$

10. $2.556$

11. $\approx 19$

12. $0.010$

13. $\$3.47$

14. $\approx 40$

15. $45.5$

Multiplying and Dividing Decimals Back to Module