Multiplying Decimals
Multiply decimal numbers in Grade 6 math by ignoring the decimal point, multiplying as whole numbers, then placing the decimal by counting total decimal places in both factors.
Key Concepts
Property The number of decimal places in a product is the sum of the decimal places in the factors.
Examples $0.5 \times 0.3 \rightarrow 5 \times 3 = 15$. Two total decimal places gives $0.15$. $0.12 \times 0.5 \rightarrow 12 \times 5 = 60$. Three total decimal places gives $0.060$ or $0.06$. $(0.4)^2 = 0.4 \times 0.4 \rightarrow 4 \times 4 = 16$. Two total decimal places gives $0.16$.
Explanation Multiplying decimals is a two step dance! First, ignore the decimal points and multiply the numbers like they're whole. Next, count the total number of decimal places in the original numbers you multiplied. Your final answer must have that same number of decimal places. Just count from the right and place your point. Easy peasy!
Common Questions
How do you multiply two decimal numbers?
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 and place the decimal that many places from the right in the product.
Why do you count decimal places instead of aligning them when multiplying?
When multiplying, you do not need to align decimal points like in addition. Instead, the number of decimal places in the answer equals the combined total of decimal places in both factors.
How do you check if your decimal is placed correctly after multiplying?
Estimate by rounding each factor to the nearest whole number first and multiplying those. Compare your estimate to the exact answer — they should be close in magnitude. If not, recheck your decimal placement.
What is a common mistake when multiplying decimals?
A frequent error is counting decimal places incorrectly or placing the decimal too early or too late in the product. Always count all digits after the decimal point in both numbers to get the correct placement.