7th grade · Math · Unit 2 of 16
Decimal Operations
Add, subtract, multiply, divide decimals
What your child practices
All four operations with decimals, estimating to check answers, ordering decimals, and money problems such as unit prices.
Arizona Academic Standards learning standard: 7.NS.A.2; 7.EE.B.3 · computing with decimals and solving multi-step problems with rational numbers
How we explain it
Children can open this short lesson before they practice.
- To add or subtract, line up the decimal points.
- Fill empty places with zeros so the numbers match.
- Then add or subtract like whole numbers.
Example: 3.45 + 2.8 = ? Write 2.8 as 2.80 and line up the points. 3.45 + 2.80 = 6.25. Answer: 6.25
Decimal Operations in Arizona
In the Arizona Academic Standards, this is unit 2 of 16 in 7th grade Math, after Add & Subtract Integers and before Fractions, Decimals & Percents.
Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.
Source: Arizona Department of Education
Sample questions
A taste of this unit. In the app, questions change every time and get easier or harder to match your child.
Question 1
Use the order of operations: what is 9.7 + 2.7 × 5?
9.7 + 2.7 × 5
- 23.3
- 51.2
- 62
- 23.2
23.2
Hint: Multiply before adding: 2.7 × 5 = 13.5. Then 9.7 + 13.5 = 23.2.
Question 2
Which is the best estimate for 79.7 × 7.2?
- 87
- 560
- 56
- 5600
560
Hint: Round each number to a friendly one: 79.7 ≈ 80 and 7.2 ≈ 7. Then 80 × 7 = 560.
Question 3
What is 2.8 × 0.4?
2.8 × 0.4 = ?
- 0.112
- 11.2
- 0.0112
- 1.12
1.12
Hint: Multiply as if there were no decimal points: 28 × 4 = 112. The factors have 2 decimal places in total, so the product does too: 1.12.
Question 4
Apples cost $5.70 per kilogram. How much do 3.5 kg of apples cost, in dollars?
answer box
19.95
Hint: Multiply the price by the mass: 5.7 × 3.5. Without decimals that's 57 × 35 = 1995; there are 2 decimal places in total, so the cost is $19.95.
Question 5
Put these decimals in order from least to greatest.
- 0.01
- 0.18
- 0.182
- 0.081
- 0.1
0.01 → 0.081 → 0.1 → 0.18 → 0.182
Hint: Compare tenths first, then hundredths, then thousandths. Writing them with the same number of places helps: 0.010, 0.081, 0.100, 0.180, 0.182.
Question 6
What is 29.9 − 18.79?
29.9 − 18.79 = ?
answer box
11.11
Hint: Line up the decimal points and fill in zeros so both numbers have the same places: 29.90 − 18.79. Subtract, regrouping where you need to: 11.11.