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How to Multiply Normal Numbers With Decimals

The easiest way to multiply normal numbers, or whole numbers, by a decimal number is to punch the numbers into a calculator. However, with one push of a wrong button, you'll end up thinking a wrong answer is the right answer. Learning how to multiply whole numbers with decimal numbers by hand is not only useful at times when you don't have a calculator on hand but helps you understand how you got your answer, which many math instructors want to see in your tests and assignments.

Instructions

    • 1

      Place the numbers in a column, with the number containing more digits on top of the other, and align the numbers to the right, not according to the decimal point (See Reference 1). For example, write 35.7 x 28 as follows:

      35.7

      x 28

      -------

    • 2

      Ignore the decimal point and multiply each digit in the bottom number with each digit in the top number starting from the right, like you would when multiplying two whole numbers. If the whole number is higher than a single digit, you will have two or more products. Align the products so that the last digit of each product is in line with the appropriate digit in the second number of the multiplication problem, as in the following example:

      35.7

      x 28

      -------

      2856

      714

    • 3

      Add the products, as in the following example:

      35.7

      x 28

      -------

      2856

      714

      -------

      9996

      If the whole number is a single digit, you can skip this calculation.

    • 4

      Move the decimal point, starting from the right of the final answer, according to the number of decimal places in the decimal number being multiplied. For example, in the problem 35.7 x 28, the decimal number contains one decimal place, so you would move the decimal point one place from the right of the final answer. Therefore, 35.7 x 28 = 999.6.

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