Multiplying Decimals
Grade 5 · Math · Study Guide
Learn to multiply decimal numbers accurately by counting decimal places.
To multiply decimals, ignore the decimal points and multiply the numbers as if they were whole numbers. Then count the total number of decimal places in both factors combined — that tells you where to put the decimal point in your answer.
For example, 0.4 × 0.3: multiply 4 × 3 = 12, then count decimal places: 0.4 has 1 and 0.3 has 1, totaling 2. Place the decimal 2 places from the right: 0.12.
When multiplying by powers of 10 (10, 100, 1000), simply move the decimal point to the right by as many places as there are zeros in the power of 10.
| Problem | Whole Number Multiplication | Total Decimal Places | Final Answer |
|---|---|---|---|
| 0.6 × 0.4 | 6 × 4 = 24 | 1 + 1 = 2 | 0.24 |
| 1.2 × 3 | 12 × 3 = 36 | 1 + 0 = 1 | 3.6 |
| 0.05 × 0.3 | 5 × 3 = 15 | 2 + 1 = 3 | 0.015 |
| Problem | Action | Answer |
|---|---|---|
| 0.34 × 10 | Move decimal 1 right | 3.4 |
| 0.34 × 100 | Move decimal 2 right | 34 |
| 0.34 × 1000 | Move decimal 3 right | 340 |
Key terms
- Factor
- A number being multiplied in a multiplication problem.
- Product
- The result of multiplying two or more numbers.
- Decimal Places
- The number of digits to the right of the decimal point in a number.
- Powers of 10
- Numbers like 10, 100, 1000 — multiplying by these shifts the decimal point right.
Practice questions
What is 0.5 × 0.4?
- 0.9
- 2.0
- 0.20
- 0.020
Show answer
Answer: 0.20
5 × 4 = 20. Total decimal places = 1 + 1 = 2. So 0.20 (same as 0.2).
What is 1.5 × 3?
- 4.5
- 0.45
- 45
- 0.045
Show answer
Answer: 4.5
15 × 3 = 45. Total decimal places = 1. Answer: 4.5.
0.06 × 0.7 = ___
Show answer
Answer: 0.042
6 × 7 = 42. Total decimal places = 2 + 1 = 3. Answer: 0.042.
2.4 × 100 = ___
Show answer
Answer: 240
Multiplying by 100 moves the decimal 2 places right: 2.4 → 240.
A bottle holds 0.75 liters. How much do 4 bottles hold?
- 3 liters
- 0.3 liters
- 30 liters
- 0.03 liters
Show answer
Answer: 3 liters
0.75 × 4 = 3.00 = 3 liters. (75 × 4 = 300, 2 decimal places → 3.00)
Fun facts
- Gas prices use decimal multiplication — if gas costs $3.45 per gallon and you buy 8.5 gallons, you multiply two decimals to find the total!
- Multiplying any decimal by 0 always gives 0, no matter how many decimal places.
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