5.2.2. Multiply Decimals

Multiply Decimals

Multiplying Decimals is very much like multiplying whole numbers - we just have to determine where to place the decimal point. The procedure for multiplying decimals is similar to multiplying fractions. To multiply fractions, you multiplying the numerators and then multiply the denominators.

There is a pattern that we can use. In the above illustration, we can see in A that we multiplied two numbers that each had one decimal place, and the product had two decimal places. In B, we multiplied a number with one decimal place by a number with two decimals places, and the product had three decimal places.

• When we multiply two numbers with decimals, we count all the decimal places in the factors to get the number of decimal places in the product.
  • i.e. 0.01 x 0.004 = 0.00004 - because 2 decimal places + 3 decimal places equals 5 decimal places.
• Once we know how to determine the number of digits have the decimal point, we can multiply the decimal numbers without converting them to fractions first. The number of decimals places in the product is the sum of the number of decimal places in the factors.

The rules for multiplying positive and negative numbers apply to decimals, as well

When you multiply signed decimals, first determine the sign of the product and then multiply as if the numbers were both positive. Finally, write the product with the appropriate sign.

Example: