Definition
Decimal multiplication
Decimal multiplication finds a product when one or more factors are written in decimal notation.
What it means
First decide what the factors mean: equal groups, part of an amount, or a scale change. Multiply the amounts, then use place value to name the result correctly. For example, six tenths taken four times makes twenty-four tenths, which is 2.4.
Remember it
Multiply the amounts; let place value set the product’s size.
Example
0.36 × 5 = 1.8. Five groups of 36 hundredths make 180 hundredths. Since 100 hundredths make 1 whole, 180 hundredths is 1 whole and 80 hundredths, or 1.80 = 1.8.
Watch for
For positive numbers, multiplying by a factor between 0 and 1 scales the other factor down, so the product can be smaller.
Common mix-up
Counting decimal places can check a written method, but place value—not moving the decimal point by guesswork—is what gives the product its value.
Exact meaning
Decimal multiplication multiplies factors when at least one is written in decimal notation. It can describe equal groups or scaling, and base-ten place value determines the size of the product.