Decimals

Note: This is NOT the video lesson page. If you are trying to watch a video lesson for homework, click here: https://sites.google.com/a/kcsd96.org/mrs-didech/lessons/video-lessons

It is important to know the name of each place value in a decimal.

Let's look at this example:

123.456789

1 - Hundreds

2 - Tens

3 - Ones

. - And

4 - Tenths

5 - Hundredths

6 - Thousandths

7 - Ten Thousandths

8 - Hundred Thousandths

9 - Millionths

Rounding:

When rounding, follow these steps:

1. Circle (circle the digit in the place value to the instructions say to round)

2. After (draw an arrow from the circled digit to the digit that comes after it)

3. Keep or Change (look at the circled digit -- if it's less than 5, keep the circled digit the same. If not, add one to the circled digit)

For example:

Round 8.379 to the nearest tenth.

1. Circle the 3, which is in the tenth place

2. Draw an arrow to the 7, which comes after the 3

3. Change the 3 by adding one to it, since 7 is greater than 5

The final answer is 8.4

Ordering:

The closer a digit is to the decimal point, the larger it is. For example, 0.1 is greater than 0.01. If two decimals are an equal number of places away from the decimal point, decide which number would be bigger if it were a whole number. For example, 0.004 is greater than 0.002 because 4 is greater than 2.

Addition and Subtraction:

Align the place values so that the decimal points line up. Then add or subtract the decimals normally. Don't forget to include the decimal point in your answer.

Multiplication:

Do a whole number estimate to make sure the decimal in your answer is in the right place. For example, if you are multiplying 7.2 and 8.3, first estimate your answer by multiplying 7 and 8. We know 7*8=56, so our decimal answer should be close to that. After multiplying 7.2 and 8.3, I get 59.76. I know the decimal point is in the right place because 59 is close to 56. If I had gotten 5.796, I would know my work would be incorrect since 5 is not close to 56.

Division:

Always align the decimal point in the quotient with the decimal in the dividend. Never work with a decimal in the divisor. Instead, move the decimal over until you have a whole number in the divisor. Then, move the decimal over the same number of places in the dividend and then start your division.

Students Teaching Students:

Saaniya (Decimal Multiplication Slide Show)

Emily and Becky (Central Tendencies, Decimal Operations, Absolute Value, OOOps Slide Show)

Tommy (Long Division Video Lesson)

Nikhil (Long Division Video Lesson)

Ben (Adding and Subtracting Decimals Video Lesson)

Maya (Adding and Subtracting Decimals Video Lesson)

Additional Resources:

Adding Decimals

http://www.khanacademy.org/math/arithmetic/decimals/v/adding-decimals (Suggested by Brynn C.)

Place Value

http://www.enchantedlearning.com/math/decimals/placevalue/