I designed this lesson to teach my kids how to determine an unknown whole number in a subtraction equation. I will teach them to draw an illustration to represent their problem and to circle partners to find out "how many more." (1.OA.A.1). By learning how to find their unknown number they will be able to increase their fluency in subtraction problems and add to their list of strategies.
They will have to make sense of their problems and continue to work until the correct answer is attained during this lesson. (MP1). This lesson is teaching them a strategy for finding an entry point for solving for an unknown by comparing numbers. It develops perseverance and encourages them to think about the task they are using to solve with.
I want to get them thinking about missing quantities. I am going to gather 5 unifix cubes, show the class and have them verify I have 5 in my hand. I will turn around and remove 2 and show them the 3 left and ask: How many did I take? Of course, they should say 2. If I have total success, I will continue with a few more of these types of problems, but if I see some students having difficulty with this task I will stop and show them what I took away. This will provide them a concrete task to see that I showed them 3 and took 2 away. 3+2=5.
Today we are going to subtract by comparing sets of numbers. I will be using ten red and ten blue unifix cubes. I will pass out copies of the worksheet from the resource section.
First, I will read the following problem to my students.
Jacob had 8 red cubes and Alex had 3 cubes. How many more cubes did Jacob have?
I will use my students names in the problems to encourage them to pay attention. I will open my interactive tools on the Smart Board and initiate a class discussion.
Students how many cubes did Jacob have? (8, I will put 8 red cubes in a row on the screen and have them draw the same picture on their worksheet)How many cubes did Alex have? (3, then I will place the 3 blue cubes next to the 8 cubes in parallel lines) What is the questions? (How many more cubes did Jacob have?) We can match one cube of Jacob's to one cube of Alex's until there are no more partners and then we will know how many more Jacob had. (I will have them do the same as me and circle each set of cubes to find partners.)
I will circle one red and one blue together so they can see where 3 sets will match as partners, but 5 are left over. I will present them how this can be written as a subtraction problem; 8-3=5. Look at the student explanation video to see the problem on the Smart Board. If I have a student who is struggling understanding this idea with just the visual being on the SmartBoard, I will pass out unifix cubes for those students to participate with me as I model.
We will go on to do 3 more problems together.
Taylor had 6 cubes and Rhiauna had 2 cubes. How many more cubes did Taylor have?
Nathan had 5 cubes and JJ had none. How many more cubes did Nathan have?
Maddox had 9 cubes and Katie had 1. How many more cubes did Maddox have?
I will have my students continue to use the Worksheet Pattern for the to organize their information and write their equations. We will continue with the same type of problems, but now they will write their own number expressions for the problems I read. I will read the following problems one at a time and give them time to work in between. I will provide cubes to anyone that needs a concrete manipulative.
Karly had 6 cubes and Matthew had 3 cubes. How many more did Karly have?
Ryan had 10 cubes and Chelsea had 3 cubes. How many more did Ryan have?
Serenity had 9 cubes and Nicholas had 8 cubes. How many more did Serenity have?
Brannon had 6 cubes and Parker had 1 cube. How many more did Brannon have?
Check out one of my little guys Solving his work video, step-by-step. I'm so proud of his hard work!
There is going to be so much hard work in this lesson, look at their little faces concentrating and waiting for our next step. They didn't get frustrated, but they were strongly engaged and challenged.
I will pass out 3x5 cards and give my students a partner. I will ask them to talk with each other about what we did today and write down their best piece of instruction they would give someone who has not done this type of math before. I will allow them 5 minutes to write down their idea then we will begin share time at the carpet.