EXT 3-6 Sampler

48 Grade5 SubtractingUnlikeFractions Objective17: To subtract fractionswithunlike denominators. Materials: FractionBars orFractionStrips (Master 16), multiple strips (made from theTableofMultiples,Master 14), 10-sideddice SubtractionwithFractionBars Writeon theboard: Youbuy 3 4 yardof fabric. Youuse 1 3 yard tomake apillow.Howmuchdoyouhave left? You live 1 9 0 kilometer from school. Youwalk 1 2 kilometer. How far are you from school? Eachproblemwill bedemonstratedwithFractionBars andmultiple strips. Each small groupwill need a set of fractionbars and aTableofMultiples (Master 14) cut into multiple strips. You cannot addor subtract fractionsunless theyare the same colororaredivided intoanequal numberof parts. Find¾and⅓.Are they the same color? (no) What color can theybe changed to? (orange) Forproblem1, change theblue¾bar intoorange 9⁄12 and the yellow⅓bar toorange 4⁄12. Writeon theboard: Howdowe find theanswer? (take away, or cross out 4of the twelfths from 9⁄12.)Cross out the 4⁄12 as shown above. What is¾–⅓? (5⁄12)Write the 5⁄12 under the equal bar. SubtractionwithMultipleStrips Cut themultiplication table intomultiple strips. Useyourmultiple strips to find the lowest common denominatorandequivalent fractions for eachpair of fractions. To subtract¾–⅓, place the3multiple stripover the 4 stripand the1 stripover the3 strip. What is the smallest commonnumber in thebottom rowof each fraction: the3and4 rows? (12) Whatnumber is above the12 in the3 row? (9) 9⁄12 is anothername for¾. What is thenumberabove the12 in the1 row? (4) 4⁄12 is anothername for⅓. Writeon theboard: Solve the secondproblemusingbothmethods.Note that the answer canbe simplified to 2⁄5. Goover theproblem at the topof thepageusing multiple strips todemonstrate. Studentsmayuse fraction bars ormultiple strips to complete thepage. DiceyDifferences Game for 2players. Players take turns throwing two10-sideddice twice and forming a fraction each timeusing the smallernumber for thenumerator and the largernumber for thedenominator. Theplayerwith the greaterdifferencebetweenhis orher fractions earns one point. For example, aplayer throwing a1 and a6on the first throw and a2 and a3on the second throwwould subtract:⅔– 1⁄6 for adifferenceof½. Skill Builders 17-3, 17-4 3 4 – 9 12 4 12 1 3 3 4 – 9 12 4 12 5 12 1 3 - Lesson12, 5ETeacherGuide 39 39 ©Math TeachersPress, Inc.,Reproduction by anymeans is strictly prohibited. SubtractingUnlikeFractions Danwalked of amile to amovie. Thenhewalked of amile toa restaurant. Howmuch farther was hiswalk to the restaurant than to themovie? Thisproblem compares two numbers,so it isasubtractionproblem. Create equivalent fractionsso theyhave a commondenominator. x2 x2 – mile = = 9. Robert ismaking cookies.He has of a cup of brown sugar.The recipe calls for of a cup of brown sugar. Does Robert have enoughbrown sugar? Explain. _____________________________________ 10. Carol jogged of amile in themorn- ingand of amile in theafternoon. Howmuch farther did she jog in theafternoon? ________ Eat at Joe’s! mile mile Solve. 11. How is subtracting fractionswith like denominators similar to subtracting fractions withunlike denominators?What must you remember when subtracting fractions withunlike denominators? 1. – 5. – 2. – 6. – 3. – 7. – 4. – 8. – 1 12 10 12 8 10 9 12 4 12 6 12 6 10 6 9 2 8 5 10 6 10 1 12 5 8 5 8 1 12 3 10 3 10 1 10 1 9 5 12 3 4 6 8 No. , which ismore than . of amile Like: youstill subtract the numerators. Unlike: youmust first finda commondenominator before you subtract the numerators. = 5.NF.1, 5.NF.2 Students relate theactivities requiring common colors toadd or subtract to amoreabstract concept: the denominator must bea common multiple.