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分数加减法练习（2）1：5/9+X=5/6 X=5/6-5/9 X=15/18-10/18 X=5/18
X-3/8=5/8 X=5/8+3/8 X=1
X-3/7=4/9 X=4/9+3/7 X=28/63+27/63 X=55/632. 1/6+5/6 - 1/9+2/9 + - +3. 4/7+1/6－3/7 =4/7－3/7+1/6 =1/7+1/6 =13/42 2－7/9－2/9 =2－（7/9+2/9） =2－1 =1 1/4+（2/5+3/4 ） =1/4+3/4 +2/5 =1+2/5 =1又2/5 3/5+7/8+2/5 =3/5+2/5+7/8 =1+7/8 =1又7/8 7/9－（1/9+1/3） =7/9－1/9－1/3 =2/3－1/3 =1/3 5/6－3/10+1/6－3/10 =（5/6+1/6）－（3/10＋3/10） =1－3/5  | 