Q&A for How to Multiply Decimals

To round a decimal, identify the desired place value and examine the digit to its right. If the digit is less than 5, round down; if it's 5 or greater, round up. 

The positions to the right of the decimal point are assigned names that correspond to the place values of whole numbers. Consequently, the initial digit to the right of the decimal point denotes tenths, followed by hundredths, thousandths, and so forth. This naming convention facilitates a systematic understanding of the fractional components in decimal numbers.

Multiply normally, then count the total number of places to the right of the decimal point (in this case, one). Place the decimal point in the product by counting one place to the left of the right-most digit.

For each 0, move the decimal point one place to the right. So, .67 x 1 = .67, .67 x 10 = 6.7, .67 x 100 = 67.

Not necessarily. Though unless something depends on exact calculations, I find rounding helpful to make the number easier to think about.

Just multiply by 3 and insert a decimal point just to the left of the right-most digit in the answer.

If the divisor has a decimal, move the decimal all the way to the right end of the divisor. Then, move the decimal in the dividend the same number of digits to the right (even if that means adding zeroes to the right end of the dividend). Then, perform long division as you normally would, with the decimal in the quotient being immediately above the decimal in the dividend.

No. Add vertically, and line up all the decimal points in a single column (including the decimal point in the sum).

That's just a natural function of the decimal system. For example, a tenth of a tenth is a one-hundredth (.1 x .1 = .01).

Multiply the first two, then the product gets multiplied by the third number.

You round numbers exactly the same way on either side of the decimal point.

Multiply the numbers together as if they had no decimal points. Once you have the product, place a decimal point four places to the left of the right edge of the product. (Four places because there is a total of four places to the right of the decimal points in the two given numbers.)

Divide the product by one of the multipliers. If the quotient equals the other multiplier, the original product is correct.

Multiply 12 by 345. In the product, have three digits to the right of the decimal point (because there is a total of three digits to the right of the decimal points in the two numbers being multiplied).

Multiply the first two, then the product gets multiplied by the third number.

Multiply 11111 by 2222. (That is 24688642.) Then move the decimal point six places to the left, because the two original multipliers have a total of six digits to the right of their decimal points. So the final product is 24.688642.

Multiply 150 by 168. Then place the decimal point to the left of the three right-most digits, because there is a total of three digits to the right of the decimal points in the two multipliers. (Yes, even the double zeroes count here, because they contribute to the degree of precision required in the answer.)

First convert the decimal to a fraction. Then multiply the two fractions together. You'll get a fraction for the answer, which you can then convert to a decimal if you so desire.

There would be four digits to the right of the decimal point in the product, because there is a total of four digits to the right of the decimal points in the two multipliers or factors.

Start by multiplying 12 by 25. That's 300. Then, because there are two digits to the right of the decimal point in 0.25 (and none in 12), move the decimal point in the product (300.) two places to the left. The final product is 3. (Note that in this example, 0.25 is equal to ¼, and 12 multiplied by ¼ is 3.)

First multiply 424 by 21. The product is 8904. Then move the decimal point three places to the left, because there are a total of three numbers to the right of the two decimal points. The final product is 8.904.

The rule is to use in your answer the same amount of precision as the least precise of your multipliers. Because 65 has no digits to the right of the decimal point, your answer should show no digits to the right of the decimal point either. Thus your answer would be 13. If the multipliers had been 65.0 and .20, your answer would have been 13.0.

Move the decimal point to the right the same number of spaces as there are zeroes in the multiple of 10. Thus, (8.15)(10) = 81.5). Another example: (91.62575)(1000) = 91625.75.

Multiplying by 0.1 is the same as dividing by 10. Merely move the decimal point one space to the left. (12.87)(0.10) = 1.287.

Multiply as you normally would, then find where the decimal point is on the decimal. Add the point to your answer by putting it in the same place.

No. If all you have is a zero to the left of the decimal point, you can leave the zero off the number and multiply as if it weren't there.

Multiply 434 by 883; that's 383222. Then place a decimal point two places to the left of the right side of the product: 3,832.22. (Two places because there is a total of two places to the right of the decimal points in the two numbers being multiplied.)

Ignore the zero to the left of the decimal point. Multiply the other number by 6. Then in the product move the decimal point two places to the left (because there are two places to the right of the decimal point in 0.06).

First count the total number of places to the right of the decimal points in both numbers. There are seven such places. Now multiply 46 by 15. That's 690. Now move the decimal point in the product to the left seven places, for a final product of .0000690 (which could be written as 0.000069).

Line the numbers up as you would if they were both whole numbers. The number with the most digits will go on top. Then, you multiply the numbers and adjust the answer (product) by adding up the total number of decimals in the problem and insert the decimal back into the answer from the right side. Example: 4 x 3.4, 34x4 = 136. There is one decimal in the problem, so put it back into the answer by inserting a decimal one digit from the last # on the right. Answer is 13.6. It's the same when multiplying large #'s. Example 9.32x399.8 = 3726.136 (3 total digits behind decimals). ***if your answer ends in a 0, still count it while adjusting.