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用简便方法计算22一(57一78)十57

22-(57-78)+57=22-57+78+57=22+78=100

=(78+22)-69+(57+43)=100+100-69

原式=78×(57-1+43) =78×(100-1) =7800-78 =7722

下面的等式各应了加法结合律运算律 78十 (22十57)=(78十22)十57

57×8-57,=57×(8-1),=57×7,=5;8×(116+78),=8×116+8×78,=12+7,=712;23×58+13×58,=(23+13)×58,=1×58,=58.

(57十78)十22 =57十(78+22) =57+100 =157 利用了加法结合律

78×42+79+79×57 =78×42+79×58 =78×42+﹙78+1﹚×58 =78×42+78×58+58 =78×﹙42+58﹚+58 =78×100+58 =7800+58 =7858

原式 =78x(57+43)-78 =78x100-78 =7800-78 =7722

57.8乘99加5.78 =58.7×100-57.8+5.78 =587-57.8+5.78 =534.98

怎么简便计算 322-143+78-57 =(322+78)-(143+57) =400-200 =200

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