EXT K-2 Sampler

53 Grade1 Lesson 8, 1ETeacherGuide 23 Objective 39, 42: Todevelopunderstanding of comparative subtraction as findinghowmany more or fewer one number is than another. Materials: Interlocking cubes, base tenunit blocks HowManyDoNot Match? The compare strategydoes not relate to the part- part-wholemodel. The task is to compare two sets to findhowmanymore or less are inone set. Itwill be helpful to rephrase these problemswith, “Howmany extras are there?” or “Howmanydonotmatch?” Identify two sets of objects in the room that canbe compared to eachother, e.g., the number ofwindows compared to the number of doors. Tell a story that would compare these two sets of objects. Example: There are 6windows inour classroom. There are 2doors.Howmanymorewindows are there thandoors? Ask a student tohelp find andunderline the question and then find and circle the facts. Ask students tomake a groupof cubes of one color for the number of windows, and a groupof cubes of another color to represent the number of doors.Have them solve the problembymatching each cube of one color to a cube of the other color. Howmany donotmatch? (4) To findhowmanymoreonenumber is than another, what operationdoweuse? (To findhowmanymore, we use subtraction.) Amost useful strategy in solving comparative subtractionproblems is todrawpictures or use models to represent the number in each set,match the objects in each set bydrawing a line between pairs, or combiningpairs of objects and then tell howmanydonotmatch. Direct attention to the example at the topof the page.Have students place a set of 7 cubes and a set of 4 cubes on their desks to represent the stamps. After studentsmatch the cubes, ask them todraw lines connectingpairs of stamps on the page so that theydevelop the concept ofmatching to solve comparative subtractionproblems. Howmanymore stamps doesMikehave? (3) Have students solve problems 1–3 alone orwith a partner. More or LessGame Give twoplayers a pile of anodd number of unit blocks, up to 25. One player separates the blocks into two almost-equal piles without actually counting them . The other player chooses the pile he or she thinks hasmore. The first player claims the remainingpile. To findwhichpile hasmore, both players simultaneouslymove 1block to the center until one player runs out. The other player says, “I had___more than you did,” andkeeps the counters remaining inhis pile. Players switch roles and repeat. The first player to keep 5 counters is thewinner. TheGame of Less is played in the sameway, except the playerwith fewer blocks keeps the counters remaining. Skill Builders 42-1, 42-2, 42-3 Conceptual Understanding Mypile hasmore! 23 ©Math TeachersPress, Inc.Reproduction by anymeans is strictly prohibited. Mike had 7 stamps. Susan had 4 stamps. Howmanymore didMike have? 7 – 4 = _____ Mike Susan Match the objects in one set to the objects in the other set. Tell howmany do not match. 1. 8 sticks of gum 6 jelly beans Howmanymore sticks of gum? ____ ____ = ____ 2. 7worms 10 birds Howmany fewer worms? ____ ____ = ____ 3. 9 TVs 4 radios Howmanymore TVs? ____ ____ = ____ “Howmanymore ” or “howmany fewer” tells you to compare the numbers by subtracting. Problem Solving Steps HowManyMore, HowMany Fewer 3 2 3 5 8 10 9 – – – 6 7 4 1.OA.1 ProblemSolvingStrategy: WriteaNumber Sentence ©MathTeachersPress, Inc. 64 Liam and Anna are buildingwith blocks. Liam’s tower is 6 blocks tall. Anna’s tower is 8 blocks tall. Liam Anna Tobeusedwith lesson 8: page23 Write + or – tomake the statement true. 8 6 = 2