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DECIMAL REVIEW - ADD - SUBTRACT - MULTIPLY

Reading and Writing Decimals


Tips to remember:

*A dot is used to represent a decimal point.

*Whole numbers precede the decimal point, and any fractional part follows the decimal point.

*Decimals are fractions divided into tenths, hundredths, or some power of 10.

*Sample of place value names:

hundred thousands - ten thousands - thousands, hundreds - tens - ones. Tenths – hundredths – ten thousandths, hundred thousandths – ten thousandths

*example: 325, 211.6849; this number is read as three hundred twenty-five thousand, two hundred eleven AND six thousand, eight hundred forty nine ten thousandths.

Note: The word “and” represents the decimal point.


Adding and Subtracting Decimals

Key: Line up the decimals

Also, whole numbers have an implied decimal behind the last digit.


Step 1 – Write the numbers vertically with the decimals lined up

Step 2 – If necessary, use zeros as placeholders

Step 3 – Add or Subtract. The decimal in the answer must line up with the decimal in the problem. In other words, one should be able to draw a straight line beginning with the decimal in the first number through the decimal in the answer.


Example: Add 23.4, 45, and 34.758


23.400 (added two zero place holders)

35.000 (…placed a decimal behind the whole number and added three zero placeholders.)

34.758

---------

89.158 Note: It is possible to draw a straight line through all of the decimals.




Multiplying Decimals:

Key: To count the total digits behind all decimal points


Step 1 - Temporarily ignore the decimal point and multiply

Step 2 – After multiplying, it’s time to replace the decimal point by counting the number of digits behind all decimal points.

Step 3 - start from the right of the product and move forward(left) the same number of times to place the decimal point.


Example: 4.56 X .3 =

Step 1: 456 x 3 = 1368

Step 2:

4.56 ( has 2 digits behind or following the decimal point)

X .3 (has 1 digit behind the decimal point)

----- Therefore, there are a total of 3 digits behind the decimal point


Step 3: 4.56 X .3 = 1.368 (The answer has 3 digits behind the decimal point)



Practice:


1) Write the numeral: three hundred sixty-two and forty-eight thousandths

2) find the sum: 67.3 + 19 + 43.211

3) find the sum: 34 + .56 + 5.32

4) Subtract 398.1 from 697.34

5) Find the product: 39 X .32

6) Find the product: 239.22 X .12




Answers:

1) 362.048

2) 129.511

3) 39.88

4) 299.24

5) 12.48

6) 28.7064

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