Subtract Away your Fears

By: Rebecca Gilroy

• Introduction: As a class we are going to review simple subtraction and start applying it to word problems.

• Subject: Second Grade Mathematics

• Topic: Subtraction

• Objectives: The students will review simple subtraction to make sure they all remember and understand subtraction. We will solve missing addend problems by counting up or subtracting.

• Procedures: The teacher will use the power point presentation as the lesson. Move through the power point as if you were writing the problems on the board. Discuss every step the students will take in solving a problem; stopping to make sure each student understands the concepts; ask questions and call on the students who are not raising their hands. At the end of the power point is a quiz; go through the quiz as a class, making sure each student arrives at the correct answer.

• Evaluation: Before-Students already know how to subtract simple problems with small numbers; we will review this concept before diving into the main lesson.

During-Asking questions during the lesson and the completion of problems on the power point. After-The quiz at the end of the power point.

• Materials: Power point presentation.

Lets Review…

What is Subtraction?

• The operation used when taking something away from a group.

• The opposite of addition.

• Represented by the - sign.

Simple Problems

7 – 2 = ? 8 – 6 = ?

4 – 4 = ? 5 – 1 = ?

5

2

0

4

Subtraction using the missing addend approach?

• What is the number, a, that would be added to a number, b, to equal a number, c.

a + b = c a = c – b b = c – a

Lets Practice…

McKenna has 3 dollars but needs 7 dollars to go to the movie.

How much more money does she need?

Take this step-by-step:

1) How do we figure out how many dollars McKenna needs?

2) She has $3 but needs $7.

3) $3 + ? = $7 OR 3 + x = 7

4) 3 + x = 7

5) x = 7 – 3

6) x = 4

Do we understand how we arrived at the answer?

YES NO

Lets try another…

Suppose you have 12 candy bars and you give away 7.

How many do you have left?

Take this step-by-step

1) How do we figure out how many candy bars we still have?

2) You have 12 candy bars but gave away 7.

3) 12 – 7 = x OR 7 + x = 12

4) 7 + x = 12

5) x = 12 – 7

6) x = 5

How about now, are you understanding? YES NO

Lets Review…

a + b = ca = c – bb = c – a

Quiz:

# 1 # 2

Question 1:

Sara has some red chips and four black chips.

She has nine chips all together.

How many red chips does she have?

5 13

Question 2:

Shauna has run two miles so far and wants to run six.

How much farther does she need to run to meet her goal?

8 4

Correct!

Great Job!

Now move onto the next one!

# 2

Incorrect

Go back and try again.

Remember: a + b = c a = c – b b = c – a

# 2

# 1

Congratulations!

You now know how to subtract using the missing addend approach.

Tomorrow we will review and then start the take home assignment.

Great Job Everyone!

References:Annenberg Media (2010). Meanings and Relationships of the Operations.

Retrieved October 6, 2010, from Learning Math Web site: www.learner.org/courses/learningmath/number/session4/part_a/subtraction.html

Chuck at SSSoftware.com (2000, October 6). Use the Language of the Operations. Retrieved October 6, 2010, from Whole Number Arithematic Online Documentation Web site: www.sssoftware.com/docs/wnadoc/language.html

DeGabriele (2008, October 8). Missing Addend Concept. Retrieved October 6, 2010, from Web site: www.ellerbruch.nmu.edu/classes/CS255f03/CS255students/adegabri/P6/MissingAddend.html

The picture is from http://powerbacks.com/sampler_thumbs/education/educationthumbsset3.htm