Multiplying Decimals. Do not line up the decimal points, just the right-most digits. Temporarily ignore the decimal points and multiply just as if you were multiplying whole numbers. Count the total number of digits after the decimal points in the original numbers.

To multiply a decimal number by a whole number, follow these steps:

1. Multiply. as you would with whole numbers.
2. Count the total number of decimal places in your factors.
3. Move the decimal point in the product one place to the left for each decimal place you counted.

Just line up the decimal points, and (if necessary) add zeros to the end of one number, so they have the same number of decimal places. Then add (or subtract) as you usually would. In your answer, the decimal point should go exactly below where it is in the numbers being added (or subtracted).

Here’s how to multiply decimals:

1. Perform the multiplication as you would for whole numbers.
2. When you’re done, count the number of digits to the right of the decimal point in each factor and add the result.
3. Place the decimal point in your answer so that your answer has the same number of digits after the decimal point.

Move the decimal point two places to the right to find the product. To multiply a decimal number by a power of ten (such as 10, 100, 1,000, etc.), count the number of zeros in the power of ten. Then move the decimal point that number of places to the right. For example, 0.054 · 100 = 5.4.

Rounding to decimal places

1. look at the first digit after the decimal point if rounding to one decimal place or the second digit for two decimal places.
2. draw a vertical line to the right of the place value digit that is required.
3. look at the next digit.
4. if it’s 5 or more, increase the previous digit by one.

Example

1. Round this number to 3 decimal places.
2. Count along the first 3 numbers to the right of the decimal point.
3. Count along the first 3 numbers to the right of the decimal point.
4. Count along the first 3 numbers to the right of the decimal point.
5. Look at the next number (the 4th number after the decimal place)

It’ll be really easy! Ignore the decimal points and multiply as usual… Count how many total digits are on the right side of the decimal points in the guys you are multiplying… Place the decimal point in your answer so there are this many digits to the right.

If you want to multiply a decimal by a whole number, just ignore the decimal point and multiply like normal! Then, bring the decimal point back for the answer.