Mastering decimals

Hi all! Today in class, we finished up with lesson 6.2 and started 6.3.

For 6.2, we learned more methods for doing operations with decimals. The all can be done by either drawing decimal units and then use different colored highlighters to shade.

For addition, all you would have to do is shade the first number on the unit and then the second on the unit. The answer would be the total amount shaded.

For subtracting decimals with decimal squares, the first number would be shaded, and then the amount being subtracted would be shaded with another color OVER the first. The answer will be the amount that is not overlapped.

subtractionThis shows the problem 1-.5.

1 is shaded on the decimal square in green, and then .5 is covered in white. The answer is .95 because is is the amount in green remaining.

Multiplying on decimal squares is similar to the overlapping model for fractions I told you about a few posts ago. To do this, you would have to shade one amount in one color, and then shade the second amount in a different color perpendicularly to the first.  An example would look like this:

multiplyThis example shows the problem .4 • .2. The overlap of the two numbers is the answer, which is .08.

Division can be done two different ways using these squares. If you are dividing a decimal by a whole number, then you would shade the decimal on the square and divide it into the an equal number of sections. The answer would be the amount in each section. Here’s what that would look like:

divide.45 is shaded on the square, and is divided into 3 equal sections. Each section has 15 hundredths shaded, so the answer would be .15.

If you divide a decimal by another decimal, then you will have to shade the first amount on the square and make sections out of that containing the amount it is being divided by. The answer will be the total number of sections. This would look like:

divide2This decimal square represents the problem .40 ÷ .20. The amount of 40 hundredths is shaded in blue, and then divided into sections of 20 hundredths. There are 2 sections, so the answer is 2.

6.3 involves percentages. To start us off in this section, we had a student presentation. She had us split into groups of 3 and play a game that was similar to Connect Four. We would spin to get a number between 1 and 10, and then take that percentage from an amount of our choosing. We then would cover a square on the board that she made up (i.e. 6% of 100=6. A square containing the number 6 would be covered). The first player to get 4 of their pieces in a row would win. I liked this game because it was fun, and it also helped us to recognize patterns of percentages.

After this presentation, we did a worksheet that involved finding percentages of prices and amounts just by finding 10% of it. For example, we would have to find 40% of $250.00. To do this in your head, you could just find 10% of $250 first. Taking 10% is just moving the decimal place two places to the left. So, in this case, 10% of $250 would be $2.50. Then, you would multiply this amount by 4 to find 40%. $2.50 • 4= $10.oo.

By knowing how to find percentages with taking 10%, you can easily calculate discounts and tips amounts in your head. So, next time you see a sale at a store, instead of calculating it on your cell phone, try to do it in your head!

That’s if for today! Next post will be after Monday’s class.

Hope the rest of your week is full of smiles!



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