Decimal Operations: Add, Subtract, Multiply, Divide — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. 0.7 × 0.9 = 0.63
The answer is 0.63. Multiply 7 × 9 = 63, then count two total decimal places in the factors to place the decimal: 0.63.
2. 2.4 × 0.3 = 0.72
The answer is 0.72. Compute 24 × 3 = 72, then place the decimal two places from the right (one from each factor) to get 0.72.
3. 1.5 × 1.5 = 2.25
The answer is 2.25. Multiply 15 × 15 = 225, then move the decimal two places left (one from each factor) to get 2.25.
4. When you multiply 0.4 × 0.2, the product has 2 decimal places.
The answer is 2. Each factor has one decimal place, and 1 + 1 = 2, so the product 0.08 needs two decimal places.
5. 3.6 × 0.5 = 1.8
The answer is 1.8. Multiplying by 0.5 is the same as taking half, and half of 3.6 is 1.8.
6. 0.12 × 0.3 = 0.036
The answer is 0.036. Multiply 12 × 3 = 36, then place three total decimal places (two from 0.12 plus one from 0.3) to get 0.036.
7. Multiplying any number by 0.1 is the same as dividing by 10.
The answer is 10. Since 0.1 equals 1/10, multiplying by 0.1 shifts every digit one place to the right, which is the same as dividing by 10.
8. 4.5 × 2.2 = 9.9
The answer is 9.9. Multiply 45 × 22 = 990, then place two decimal places to get 9.90, which simplifies to 9.9.
9. If both factors are less than 1, the product is always less than either factor.
The answer is "less." Multiplying by a number smaller than 1 shrinks the other factor, so when both are below 1 the product ends up smaller than either one.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each item to its correct answer.
0.5 × 0.6
→ 0.30
0.81
1.3 × 0.4
→ 0.52
2.0
2.5 × 0.8
→ 2.0
0.52
0.9 × 0.9
→ 0.81
0.30
Correct matches: 0.5 × 0.6 → 0.30; 1.3 × 0.4 → 0.52; 2.5 × 0.8 → 2.0; 0.9 × 0.9 → 0.81.