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125x257+25X67简便计算第2道20002001X20012000-20002000X20012001第3道12+123+234+345+456+567+678+789+890+901谢谢

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答案和解析
125x257+25X67
=25×1285+25×67
=25×(1285+67)
=25×1352
=25×4×338
=100×338
=33800
20002001X20012000-20002000X20012001
=20002001X20012000-20002000X20012000-20002000
=(20002001-20002000)X20012000-20002000
=20012000-20002000
=10000
12+123+234+345+456+567+678+789+890+901
=(1+2+3+4+5+6+7+8+9+0)×111
=45×111
=4995