Subtraction from Addition

Transcription

1 Subtraction from Addition Objectives To review the and 1 shortcuts; and to guide children to identify the subtraction facts related to given addition facts. epresentations etoolkit Algorithms Practice EM Facts Workshop Game Family Letters Assessment Management Common Core State Standards Curriculum Focal Points Interactive Teacher s Lesson Guide Teaching the Lesson Ongoing Learning & Practice Differentiation Options Key Concepts and Skills Practice [Operations and Computation Goal 1] Use dominoes to model related addition and [Operations and Computation Goal 1] Identify and use patterns to solve [Patterns, Functions, and Algebra Goal 1] Use symbols to write number sentences for fact families. [Patterns, Functions, and Algebra Goal 2] Key Activities Children make up and share number stories that are solved by subtraction, discover and practice the and 1 shortcuts, and use dominoes to generate related addition and 1 2 Practicing Addition and My Reference Book, pp. 2,, 1 and 1 per partnership: each of number cards (from the Everyday Math Deck, if available) Children review addition and subtraction facts by playing Addition Top-It and Subtraction Top-It. Math Boxes 2 Math Journal 1, p. Children practice and maintain skills through Math Box problems. Home Link 2 Math Masters, p. 1 Children practice and maintain skills through Home Link activities. READINESS Exploring Domino Facts Math Masters, p. 2 dominoes Children explore the relationship between addition and subtraction facts using a concrete model. ENRICHMENT Exploring Dice Subtraction with Negative Differences Math Masters, p. dice number line Children use dice combinations to explore differences and patterns in single-digit subtraction. Ongoing Assessment: Recognizing Student Achievement Use an Exit Slip (Math Masters, page 1). [Patterns, Functions, and Algebra Goal ] Key Vocabulary subtraction number story facts 1 facts shortcut 1 shortcut Materials Math Journal 1, p. Home Link 2 Math Masters, p. 1 1 domino per child slate counters and cubes (optional) Advance Preparation Teacher s Reference Manual, Grades 1 pp. 1, 1 Lesson 2 1

2 Getting Started Mathematical Practices SMP2, SMP, SMP, SMP, SMP Content Standards 2.OA.1, 2.OA.2, 2.NBT., 2.MD. Mental Math and Reflexes Pose doubles-plus-1 and doubles-plus-2 facts. Suggestions: =? =? 1 =? 1 =? 1 =? 1 =? 1 =? 1 =? 1 =? 1 Math Message Make up a story for the number model - =. Home Link 2 Follow-Up Check that children were able to find the correct path from the child to the ice-cream cone. NOTE Change-to-less (also called take-away or taking-from) is the meaning of subtraction most often encountered in schoolwork. The comparison meaning of subtraction does not involve take-away, because nothing is actually taken away; the two sets of quantities are just being compared. Children are not expected to categorize subtraction stories as change-to-less or comparison at this time. 1 Teaching the Lesson Math Message Follow-Up Write - = on the board. Ask children to share their subtraction number stories. Draw an empty unit box. Have children suggest a label for each number story and write it in the unit box. Expect most of the children s number stories to be one of two types: Change-to-Less Start with a number of items. Decrease the number of items. Find out the number of items after the number is decreased. For example: Tavon had model cars. He lost model cars. How many model cars does Tavon have now? model cars 1 2 Change-to-Less Children can model change-to-less number stories by representing the number in the story with counters. They remove the appropriate number of counters as described in the story. The number of counters remaining is the difference. They can also model the story on a number line by starting at the number showing the number of items and counting back the appropriate number of spaces as described in the story. The number they land on is the difference. (See margin.) Comparison difference 1 2 difference Comparison Two separate quantities are known. Compare them by finding the difference between them. Tell how many more or less. For example: Supat has model cars. Neal has model cars. How many more model cars does Supat have? more model cars Children can model comparison number stories with sets of cubes, each representing the numbers being compared. They determine the answer by visually comparing the two sets of cubes. They can also model the story on a number line. (See margin.) 2 Unit 2 Addition and

3 Discussing the - and the -1 Shortcuts Write some - facts and -1 facts on the board; do not include the differences. Use both horizontal and vertical forms. Examples: - = = = - Ask children to copy and complete the facts on their slates. See whether they can describe the - shortcut and the -1 shortcut. If is subtracted from any number, that number does not change. If 1 is subtracted from any number, the result is the next smaller number. Write this problem on the board: - =. After a volunteer has given the answer, ask someone else to check the answer on a calculator. Try several other examples with 2- and -digit numbers, and with some large numbers, just for fun! Follow the same procedure with several -1 examples. Use 2- and -digit numbers and a few large numbers. Using Dominoes to Generate Related Addition and Draw a domino on the board. Help children discover a set of related facts shown by the domino. For example, for a domino with dots on one half and dots on the other, ask: What is the total number of dots shown? Which addition facts describe this domino? = and = Remind children about turn-around facts. PROBLEM SOLVING Write the numbers,, and on the board. Then write the two addition facts just named: = and =. Which subtraction facts can you write using the three numbers,, and? - = and - = Write these two subtraction facts on the board. Continue with other domino examples in the same way. - Adjusting the Activity So children can recognize the subtraction facts using dominoes, have them erase or cover up one side of the domino. For example: Nine dots in all. Take away the dots on one side by erasing them. Four dots remain. So, - =. Date AUDITORY KINESTHETIC TACTILE Domino Facts Time VISUAL For Problems 1 through, write 2 addition facts and 2 subtraction facts for each domino Student Page Write one addition fact and one subtraction fact Math Journal 1, p. EMcuG2MJ1_U2_21_2.indd 1// :1 PM Lesson 2

4 Date 2 Math Boxes 1. Fill in the missing numbers Write the sums. = 1 = = = Unit. Put an X on the digit in the tens place. Math Journal 1, p. Student Page Time 2. What is the temperature? Fill in the circle next to the best answer. F A degrees B 2 degrees C 2 degrees D degrees. Write these numbers in order from smallest to largest. Begin with the smallest number. 1, 1,,. What time is it? : What time will it be in 1 minutes? : 1 1,,, Practicing Domino Facts (Math Journal 1, p. ) Children write the addition and subtraction facts generated by each domino pattern on the journal page. The final problems include special features that may cause some children difficulty. The double- domino has only two related facts, not four: = 1 and 1 - =. The domino with dots on the top and zero dots on the bottom may confuse children. Make sure children realize that the blank half of the domino stands for zero. The four related facts for this domino are =, =, - =, and - =. Ongoing Assessment: Recognizing Student Achievement Exit Slip Use an Exit Slip (Math Masters, page 1) to assess children s understanding of the turn-around facts. Give each child a domino. Have them write two addition and two subtraction facts for that domino. Children are making adequate progress if they can write the corresponding addition problem and the turn-around fact. Some children may be able to successfully write two corresponding subtraction problems. [Patterns, Functions, and Algebra Goal ] 2 Ongoing Learning & Practice HOME LINK 2 Domino Facts Family Note Home Link Master Today we learned that addition problems and subtraction problems are related. For example, = can be rewritten to show two related subtraction facts: - = and - =. Each domino shown below can be used to write 2 addition facts and 2 related 2 Please return this Home Link to school tomorrow. Write 2 addition facts and 2 subtraction facts for each domino Practicing Addition and (My Reference Book, pp. 2,, 1, and 1) PARTNER Children practice addition and subtraction facts by playing Addition Top-It and Subtraction Top-It. Provide time for children to play both games. Children were introduced to Addition Top-It in Lesson 1-. For instructions, see My Reference Book, pages 2 and. Subtraction Top-It is played similarly. See My Reference Book, pages 1 and 1. Read the rules with the class and model a round or two prior to having children play in partnerships or small groups Math Boxes 2 (Math Journal 1, p. ) Write the sums. Tell someone at home what you know about doubles-plus-1 and doubles-plus-2 facts.. = 1. 1 =. =. = Unit Mixed Practice Math Boxes in this lesson are paired with Math Boxes in Lesson 2-. The skills in Problems and preview Unit content. Math Masters, p. 1 Unit 2 Addition and

5 Home Link 2 (Math Masters, p. 1) Home Connection Children use dominoes to generate and solve related addition and Children also practice doubles-plus-1 and doubles-plus-2 facts. Teaching Master 2 Domino Facts Fill in the missing dots and missing numbers for each problem below. Hint: You can look at dominoes to help you figure out what the dots look like Differentiation Options Make up one of your own.. Answers vary. READINESS Exploring Domino Facts (Math Masters, p. 2) 1 Min To explore the relationship between addition and subtraction facts using a concrete model, have children use dominoes to model facts. Children complete Math Masters, page 2. When they have finished the page, discuss when they added and when they subtracted to find the missing numbers. (Note that some children may add up instead of subtracting when solving the domino problems.) Explain when you think subtraction facts might help you solve the problems above. Sample answer: When I know the total number of dots and the number of dots on half of the domino, I can subtract to find the other number of dots. Math Masters, p. 2 ENRICHMENT Exploring Dice Subtraction with Negative Differences (Math Masters, p. ) 1 Min To apply children s understanding of subtraction, have them solve randomly generated single-digit subtraction problems. They record their work on Math Masters, page. Discuss the patterns they see on the page. When the two numbers are switched in the problem, the differences are the same distance from zero on the number line. When you subtract the larger number from the smaller number, the difference is a negative number. Planning Ahead If children have not cut out the Fact Triangles from Activity Sheets 1 and 2, have them do that soon. They will be used in Lesson Dice Subtraction For each problem below: 1. Roll two dice. 2. Record the numbers you rolled.. Write two subtraction number models for the numbers you rolled.. Use a number line to solve your problems. (Hint: Sometimes your answers will be negative numbers.) Example: I rolled and. = 1 and = I rolled and. 2. I rolled and.. I rolled and. Teaching Master Each time you roll the dice, how could you use one of your subtraction problems to help you solve the other? Sample answer: Each answer will be the same distance from on the number line. Math Masters, p. Lesson 2