Multiplying and Dividing Decimal Numbers
Grade 8 math lesson on multiplying and dividing decimal numbers including placement of the decimal point. Students learn to multiply decimals by ignoring the decimal point during multiplication then placing it correctly in the product, and to divide decimals by moving decimal points.
Key Concepts
New Concept When dividing by a decimal number we take an extra step to make an equivalent problem in which the divisor is a whole number. What’s next Next, you’ll master these skills through worked examples on multiplication and division, including word problems about cost and miles per gallon.
Common Questions
How do you multiply decimal numbers?
Multiply as if there are no decimal points, then count the total decimal places in both factors and place the decimal point that many places from the right in the product. For example, 2.3 x 1.4: 23 x 14 = 322, two decimal places, so 3.22.
How do you divide decimal numbers?
Move the decimal point in the divisor to make it a whole number. Move the decimal in the dividend the same number of places. Divide normally. For example, 6.4 / 0.8 = 64 / 8 = 8.
How do you place the decimal point when multiplying?
Count the total number of digits after decimal points in both numbers being multiplied. The product must have exactly that many digits after its decimal point. This ensures the magnitude of the answer is correct.
Why do we move decimal points when dividing?
Moving the decimal in both dividend and divisor by the same amount is equivalent to multiplying both by the same power of 10, which does not change the quotient. It simplifies division by creating a whole number divisor.