How to Multiply Decimals

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Mathematics, Operations (+, -, x, /, etc.), Fractions

Grade 5- 8

Objective

Students learn how to multiply decimals.

Directions

Facts to Know
You multiply decimals the same way you multiply whole numbers. Also, the decimal points do not have to be lined up. However, you must be careful to correctly place the decimal point in the product for multiplication. The number of decimal places in the answer must equal the total number of places to the right of the decimal point in the problem.
Decimal Points in the Final Answer
Multiplying decimals is the same as multiplying whole numbers. The key is to count the decimal places in each factor.
Sample: 458 x 7.3 = ?
Step 1 Line up the digits.
Step 2 Multiply as with whole numbers.
Step 3 Count the decimal places in each factor. The product must have an equal number of decimal places as the problem.
45.8
x 7.3
____
1374
+ 32060
3,343.4

Zero as a Place Holder
Remember, the product has the same number of decimal
places as the factors. Sometimes you have to add zeros as needed.
21.45
x 0.0321
_______
2145
42900
+ 643500
0.688545

Multiplying Decimals by Whole Numbers

When multiplying decimals by whole numbers, counting off decimal places is the key.
Sample: One inch contains 2.54 centimeters. How many centimeters are there in four inches?
You must multiply the number of centimeters in one inch by four.
Step 1 Line up the numbers for easy multiplication. You don't need to line up the decimal points, however.
Step 2 Multiply the numbers as you would multiply whole numbers.
Step 3 Count the number of decimal places in both numbers that you multiplied. Make sure the decimal places in the product equal the number of decimal places in the problem.
2.54 (2 decimal places)
x 4 (0 decimal places)
____
10.16 (2 decimal places)

So the final answer is 10.16 cm

Resources

  • Multiplying Decimals activity sheets
  • pencils

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