Decimal Operations: Add, Subtract, Multiply, Divide — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. 8.47 rounded to the nearest whole number is 8.
The answer is 8. The tenths digit is 4, which is less than 5, so 8.47 rounds down to 8.
2. To estimate 6.82 + 5.19, round each and add: 7 + 5 = 12.
The answer is 7 + 5 = 12. Rounding 6.82 up to 7 and 5.19 down to 5 gives a quick sum of 12, close to the exact answer of 12.01.
3. 14.35 rounded to the nearest tenth is 14.4.
The answer is 14.4. The hundredths digit is 5, so the tenths digit rounds up from 3 to 4, giving 14.4.
4. An estimate for 9.7 × 3.1 using rounding is about 30.
The answer is 30. Rounding 9.7 to 10 and 3.1 to 3 gives 10 × 3 = 30, a reasonable estimate near the exact product of 30.07.
5. 2.951 rounded to the nearest hundredth is 2.95.
The answer is 2.95. The thousandths digit is 1, which is less than 5, so the hundredths place stays at 5 and the number rounds to 2.95.
6. To estimate 20.3 − 11.8, round each to get 20 − 12 = 8.
The answer is 20 − 12 = 8. Rounding 20.3 down to 20 and 11.8 up to 12 gives 20 − 12 = 8, close to the exact difference of 8.5.
7. When a digit in the rounding place is 5 or more, you round up.
The answer is "up." The rounding rule says digits 5 through 9 push the place to the left up by one, while digits 0 through 4 leave it unchanged.
8. An estimate for 48.6 ÷ 5 using a compatible number is about 10.
The answer is 10. Replacing 48.6 with the compatible number 50 makes the division easy: 50 ÷ 5 = 10.
9. 0.867 rounded to the nearest tenth is 0.9.
The answer is 0.9. The hundredths digit is 6, which is 5 or more, so the tenths place rounds up from 8 to 9.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each item to its correct answer.
Estimate 3.9 + 8.2
→ 12
9
Estimate 15.4 − 6.8
→ 8
24
Estimate 4.1 × 5.9
→ 24
8
Estimate 27.3 ÷ 3
→ 9
12
Correct matches: Estimate 3.9 + 8.2 → 12; Estimate 15.4 − 6.8 → 8; Estimate 4.1 × 5.9 → 24; Estimate 27.3 ÷ 3 → 9.