Understand subtraction as an unknown-addend problem. For example, subtract 10 – 8 by finding the number that makes 10 when added to 8.

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Understand subtraction as an unknown-addend problem. For example, subtract 10 - 8 by finding the number that makes 10 when added to 8.
Understand subtraction as an unknown-addend problem. For example, subtract 10 - 8 by finding the number that makes 10 when added to 8.
Understand subtraction as an unknown-addend problem. For example, subtract 10 - 8 by finding the number that makes 10 when added to 8.
Understand subtraction as an unknown-addend problem. For example, subtract 10 - 8 by finding the number that makes 10 when added to 8.

Increasing Rigor

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  • Sarah picked three apples from the tree. Sarah needs 15 apples in all. How many more apples does Sarah need to pick?
  • There were 12 children on the swim team. Four of them were boys and some were girls. How many girls were on the swim team?
  • The zoo keeper gave some bananas to the monkeys for lunch. The monkeys ate 7 bananas and the zoo keeper counted 8 left. How many bananas did the zoo keeper start with?
  • Marty has 9 books in his library. He wants to have 18. How many more books does Marty need to get?
  • Ms. Smith has 17 stamps left in her book of 20. How many stickers did she use?

About the Math

It is important for students to share, discuss and compare their strategies as a class. Students will use the relationship bet

ween addition and subtraction as a strategy to solve unknown-addend problems. Students naturally connect counting on to solving subtraction problems. For the problem “15 – 7 = ?” they think about the number they have to add to 7 to get to 15. First graders should be working with sums and differences less than or equal to 20 using the numbers 0 to 20.

Provide multiple opportunities for students to study the relationship between addition and subtraction in a variety of ways, including games, modeling and real-world situations. Students need to understand that addition and subtraction are related, and that subtraction can be used to solve problems where the addend is unknown. Essential vocabulary for this standard includes: Addition, add, subtraction, subtract, and addend (online dictionary, HCPSS Vocabulary Cards).

The Illustrative Mathematics tasks below demonstrate expectation for this standard.

Rich Tasks for Multiple Means of Engagement, Expression, and Representation (UDL)

Missing-Part Subtraction:
A fixed number of counters is placed on a mat making sure that both students know the quantity (the total). One child separates the counters into twp parts while the other child hides his or her eyes. The first child covers one of the two parts with a sheet of tagboard, revealing only the other part. The second child says the subtraction sentence. For example, "Nine minus four (the visible part) is five (the covered part). The covered part can be revealed if necessary for the child to say how many there are. Both the subtraction equation and the addition equation can then be written.

Grab-Bag Subtraction:
Materials: a collection of cubes and 1 paper bag per pair of students.
Instructions:
  1. Select a number of objects for the students to work with. Player 1 fills the bag with that number of cubes.
  2. Player 2 reaches in and removes some cubes, showing player 1 how many he or she has taken.
  3. Both players predict how many cubes are still in the bag and then check their predictions.
  4. Each player records the number sentence in his or her journal ( ex. 15 - 7 = 8).

Journal Prompt:

Emily had to find the missing number in this number sentence:
17 - __ = 9
Find the missing number. Describe how you found the answer. Or draw a picture that show how you found the answer.
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Print Resources:

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Math Intervention-Building Number Power
PreK-2 (115--117)

Web Resources:

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Games and Centers
Lessons
Student Resources
Video Segments
Printables
Ten Frame Subtraction
Subtract from Ten
Missing Addend Cards

Center Ideas
Subtraction Games

Online GamesMinus MissionTen FrameFive FrameSomething's MissingMissing
Lesson Plans
Missing Part Subtraction
Try For Five
Fact Family Fun
How Many Left?
Finding Fact Families
Macaroni Math
Detectives are on the hunt for parts of 6 and 7!



Lesson Seeds
Flash a Ten Frame
A Sense of Ten
Printable Tools

Missing Part Grab Bag
Missing Addend Grab Bag (Michelle Glenn, CLES)




Questions/Comments:

Contact John SanGiovanni at jsangiovanni@hcpss.org.


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Howard County Public Schools Office of Elementary Mathematics Curricular Projects has licensed this product under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.