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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


Mastering Essential Math Skills: Decimals and Percents




Answers:
1) 362.048
2) 129.511
3) 39.88
4) 299.24
5) 12.48
6) 28.7064

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