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6： 2/7+3/8+5/8 2/7+3/8+5/8 =2/7+﹙3/8+5/8﹚ =16/56+21/56+35/56 =2/7+1 =72/56 =9/7 ﹙1又1/2﹚ =9/7 3/7+5/6+4/7 3/7+5/6+4/7 =3/7+4/7+5/6 =18/42+35/42+24+42 =1+5/6 =77/42 =11/6 ﹙1又5/6） =11/6 运用律简便 7： 结果都1/6 8： 3/10+3/4+7/10 =3/10+7/10+3/4 =1+3/4 =7/4 5/6+2/5+1/6+3/5 =﹙5/6+1/6﹚+﹙2/5+3/5﹚ =1+1 =2 5/9+﹙4/5+4/9﹚ =5/9+4/9+4/5 = 1+4/5 =9/5 5/6+﹙1/6+5/9 =5/6+1/6+5/9 =1+5/9 =14/9 9： 1/2+x=1 x=1--1/2 x=1/2 x--3/7=1/2 x=1/2+3/7 x=13/14 x+2/3=7/6 x=7/6--2/3 x=1/2 10： 1--1/3--1/4 =1--4/12--3/12 =5/12 思考题 7/8 15/16 31/32 127/128 | 