Multiply decimals
Key Notes:
1. Understanding Decimals
- A decimal is a number with a decimal point (e.g., 3.45, 0.78).
- The place values after the decimal are tenths, hundredths, thousandths, etc.
2. Steps for Multiplying Decimals
- Ignore the decimal points and multiply the numbers as if they were whole numbers.
- Count the total number of decimal places in both numbers.
- Place the decimal in the product, ensuring it has the same number of decimal places as the total counted.
3. Examples
- Example 1: 2.5×1.2
- Multiply: 25×12=300
- Total decimal places: 2
- Final answer: 3.00 or 3
- Example 2: 0.04×0.3
- Multiply: 4×3=12
- Total decimal places: 3
- Final answer: 0.012
4. Multiplying by Powers of 10
- Multiplying by 10, 100, 1000 shifts the decimal to the right.
- 3.45×10=34.5
- 3.45×100=345
5. Word Problems Example
- A book costs $3.75. If you buy 4 books, what is the total cost?
- 3.75×4=15.00
- Answer: $15.00
Learn with an example
▶️ Use the grid to fill in the missing number.
0.9 × 0.8 =
9 columns are shaded. The columns represent 9 tenths, or 0.9.
8 rows are shaded. The rows represent 8 tenths, or 0.8.
72 squares are shaded in both colours. These squares represent 72 hundredths, or 0.72.
The multiplication number sentence is:
0.9 × 0.8 = 0.72
0.72 is the missing number.
▶️ Use the grid to fill in the missing number.
0.8 × ___ = 0.08
8 columns are shaded. The columns represent 8 tenths, or 0.8.
1 row is shaded. The row represents 1 tenth, or 0.1.
8 squares are shaded in both colours. These squares represent 8 hundredths, or 0.08.
The multiplication number sentence is:
0.8 × 0.1 = 0.08
0.1 is the missing number.
🔥Use the grid to fill in the missing number.
______ x 0.3 = 0.27
9 columns are shaded. The columns represent 9 tenths, or 0.9.
3 rows are shaded. The rows represent 3 tenths, or 0.3.
27 squares are shaded in both colours. These squares represent 27 hundredths, or 0.27.
The multiplication number sentence is:
0.9 × 0.3 = 0.27
0.9 is the missing number.
Let’s practice!
