## Saturday, February 11, 2012

### Subtraction

Day 1: M&M Subtraction

Give each student small handful of M&M’s, then eat a few and write a number sentence. Repeat. Read first few pages of M&M book. Split into 2 groups, give each group a large amount of M&M’s, have them sort by color. Once that is done, have them compare. “Which set has less than another set there? You can think of subtracting as comparing different sets of objects. (prior knowledge) Find out which color set has more than another. Which has fewer?” Put up first clue word for the week and let them know when they see this word that is a hint that they will be subtracting.

Make a few number sentences using greater than and less than sign. When comfortable with that, move on to subtraction sentences. (pages 10-17) Use M&M sheets to make their own subtraction sentences with a partner—encourage to double digit..

Day 2: How Many in the Cave?

You want your students to be successful with one or two strategies that make sense to them. The strategy that will be introduced in the lesson is “Counting Up”. Counting Up is a natural strategy for students to use, because many of them solve basic subtraction facts using this method. An example would be 13 – 5 =? Students think 5 plus what number equals 13? When a student uses this strategy with larger numbers, he/ she has to break the steps into smaller pieces.
“Who likes tricks to help solve a math problem”? I am going to teach you a trick to use in subtraction called “Counting up”. Write a simple problem on the board like 5-3=2. Demonstrate counting up, do more examples making it more complex. Tell them we will be playing a game called “How Many in a Cave?” and you want them to try this strategy when they are playing.

Give each pair of students a specific number of counters and one cup.
While one student covers his/her eyes, the other student takes some of the counters and places them in the “cave” (under the cup).
The student who was covering his/her eyes then tries to guess the number of counters in the cave.
Students determine this because they know the number they started with and they can see the number that is not in the cave.
Players switch places and the game continues.

Day 3: Missing Numbers

Explain the purpose of the shapes by doing a role-play.
Pick a group of students to be in the role-play and explain the role-play to them in the hall.
One of the students will be the teacher. The teacher will tell the group of role players to line up. You are going to line up with them as a student, but when everyone is in line, you are going to say that you forgot something and have to go get it. You will ask whoever is standing in front and in back of you to save your place. Tell the students that if you ask them to save your place they should say yes but as soon as you get out of line they should move up and take your place.
Go back into the room and have the “teacher” go up to the front and tell the group to line up.
Line up with the students you picked to help.
Pretend you forgot something so you have to get out of line to get it.
Ask the students in front and behind of you to save your place.
Leave the line and go get the thing you forgot. When you return, act upset because your place is gone and you don't know where you were supposed to be.
Redo the role-play but this time when you leave, put something in your place like a chair or a book.
Explain that the chair, or book, represents you while you are gone, and when you get back you will take the object away and get back in place.
Leave to get what you forgot and come back happy because you can take your place back.
Explain that numbers need something to hold their place in line also. Any shape can be used to represent a number that is missing from the sentence.
Brainstorm shapes, pull them out.
Write any math sentence on the board. Have the students put their heads down and close their eyes.
While their eyes are closed, put a shape over any number.
Tell the students to put their heads up and figure out what number the shape is representing.
Lift the shape off the number to see if they were right.
Do more examples. For a challenge, have students close their eyes while you write the whole sentence so they have to figure out the missing number.
For practice, do Missing Number sheet.

Day 4: How Much is Your Name Worth?

Students do subtraction problems on the worksheet for each letter of their name to find out how many points their name is worth. After they do their name, they can do their last name, partner, etc.