Our focus is shifting to working with decimals and all operations. Today, we focused on the addition and subtraction of decimals. In fact, all of our activities centered around this idea.
We began with a "Would You Rather" question:
Next, our estimation180 prompt was also about pennies:
I wanted to do a little formative assessment about student's prior knowledge of adding and subtracting decimals, so I began with a common misconception. The misconception that I see in student work is that decimal placement is not important. I have many students who do not line up the decimal. So, I began with a formative assessment. I had the students use a "quick code" to logon to goformative.com and complete the following problem:
Students used the "pen" to write the numbers on the grid (one digit per box), line up the decimal points and subtract. While I did have a number of students complete this formative assessment correctly, I also had a number who made common errors:
- This student knew where to place the decimal on a whole number, but did not put in zero place holders so that he did not subtract correctly, he just brought down the digits.
- This student forced the numbers to fit in a way that made sense to her. She did not know where the decimal point went on a whole number.
What I like about goformative.com is that you are seeing student work in real time and can work with students immediately to correct errors. To go over some of the errors, I used the idea of "My Favorite No." This is a procedure where incorrect student work (anonymous) is shown to the entire class and the class works together to make the corrections. I want students to understand that making mistakes grows our brains and to be comfortable with making AND correcting mistakes.
After completing my own version of "my favorite no," I had the classes take a few notes about adding and subtracting decimal numbers. These notes included a few new vocabulary words:
To finish out our math class, I introduced my classes to 3 Act Math. While not all of the activities can be used in my classroom because they are for higher math classes, there are a few sites that I really enjoy that employ this technique:
The activity I used today came from "Mr. Kraft's Wikispace." It is titled Cheap Chicken Sandwich. Basically, the students were to determine if the "meal deal" was the best way to purchase a chicken sandwich, fries, and drink. This type of problem solving is also similar to working with perplexities, which is also discussed by Dan Meyer on various internet sites.
I have my own version of 3 Act Math:
- Act 1 - Question
- Students see the problem in an engaging manner and develop the question that is to be solved.
- Act 2 - Gather Information
- Students determine the information they need to solve the problem and then finds the information.
- Act 3 - Resolution (Attack)
- Students use their information to solve the problem.
We discovered that, in this case, it would be cheaper to purchase the items individually!