This unit will focus on Addition, Subtraction, Multiplication, and Division of Decimals. Within that focus, we will also cover (1) using rounding to estimate sums and differences and (2) metric measurement. The metric measurement connects directly to multiplying and dividing by powers of ten.
We don't have much class time for practicing rounding numbers, so here is a game to help students practice rounding whole numbers and decimals: Soccer Math
We don't have much class time for practicing rounding numbers, so here is a game to help students practice rounding whole numbers and decimals: Soccer Math
Addition
The students have already been practicing the basic addition and subtraction on their Daily 5 reviews, and they covered it in 4th grade as well. With addition, they simply have to remember to line up the decimal points on each addend and to place it in the sum- otherwise, nothing changes from regular addition! (examples from CoolMath.com)
Practice Game: Hoop Shoot
Practice Game: Hoop Shoot
Subtraction
With subtraction, some of the problems will work the same as subtraction in past year, as long as students remember to line up the decimals and place them in the answer. However, in some problems, students will have to add a decimal point to a whole number, or have to add additional zeroes in order to regroup.
Rounding to Estimate
With Rounding to Estimate, students will need to round each number to the nearest whole number BEFORE adding or subtracting.
Example 1:
Example 2:
Multiplication
In this section, students will be expected to multiply decimals. More specifically, they will expected to:
Below is an example from CoolMath.com of how to multiply a decimal by a whole number. A more detailed explanation from CoolMath.com can be found here. A video tutorial from Math Playground can be found here.
- Multiply any decimal by 10, 100, or 1000
- Determine the placement of the decimal point using estimation
- Multiply a decimal (up to hundredths) by a whole number
- Multiply a decimal by a decimal
Below is an example from CoolMath.com of how to multiply a decimal by a whole number. A more detailed explanation from CoolMath.com can be found here. A video tutorial from Math Playground can be found here.
Below is a model for multiplying decimals. I will briefly mention it in class and show how it works, but we will not study this method in depth and it will not be on the final assessment.
Division
If the students remember how to do regular long division, then dividing decimals is simple! You can go to the CoolMath.com page here to see the details and for more examples, but an example of the expectations for our students is below.
Dividing by Powers of Ten
To divide by 10, 100, or 1000, simply move the decimal point to the left as many spaces as there are zeros. It is a shortcut to using long division or repeated subtraction. Here is a video with examples:
(YouTube video by JoAnns School. Direct link here.)
Estimation & Decimal Placement
Students can use estimation to determine the placement of a decimal in an answer. For example, in the problem 11.95 ÷ 1.9 = 6 2 8 9, where should the decimal be placed? If you round to 12 and 2, you can use 12 ÷ 2 = 6 to determine that it should be placed between the 6 and 2 to make 11.95 ÷ 1.9 = 6 . 2 8 9.
Metric Measurement
This unit will include metric measurement since multiplying and dividing by 10, 100, and 1000 are a major foundation of metric conversions. These conversions will be embedded into some of the word problems on the assessment. Below are the conversions that the students will be expected to be able to use: