Overview
This lecture explains how to multiply decimal numbers with up to two decimal places, including practical steps and examples, and practice problems.
Multiplying Decimals: Steps & Rules
- Multiply decimal numbers as if they are whole numbers, ignoring the decimal point at first.
- Count the total number of decimal places in all factors.
- Place the decimal point in the product so it has the same number of decimal places as the sum from the factors.
- When multiplying a decimal by a whole number, the product has the same number of decimal places as in the decimal factor.
Example Problems & Solutions
- Example: 58.00 × 3.00 – Multiply as whole numbers (5800 × 300), then count 4 decimal places (2 from each factor) in the product.
- Practice: For each multiplication, total the decimal places in the factors and count from the right in the product to place the point.
- Sample answers (from learning tasks):
- 3.53 × 1.25 = 4.4125
- 2.32 × 2.31 = 5.3592
- 2.42 × 1.56 = 3.7752
- 0.85 × 0.54 = 0.4590
- 0.15 × 0.55 = 0.0825
Special Cases
- If multiplying by a whole number, only consider decimal places from the decimal factor.
- In word problems, write the answer with correct units, placing the decimal correctly as calculated.
Practice Word Problems
- Beach house rental: 1,550.50 × 5 = 7,752.50 pesos.
- Jeweler: 0.6500 × 0.600 × 3 = 1.17 g of gold used.
Key Terms & Definitions
- Decimal Place — The position of a digit to the right of a decimal point.
- Factor — A number being multiplied.
- Product — The result of multiplication.
- Multiplicand — The first number in multiplication.
- Multiplier — The second number in multiplication.
Action Items / Next Steps
- Complete all assigned practice problems in your notebook.
- Review the steps for multiplying decimals.
- Prepare for a quiz on multiplying decimals next session.