用简便方法计算:123+234+345+456+567+678+789急
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用简便方法计算:123+234+345+456+567+678+789急用简便方法计算:123+234+345+456+567+678+789急用简便方法计算:123+234+345+456+567+
用简便方法计算:123+234+345+456+567+678+789急
用简便方法计算:123+234+345+456+567+678+789急
用简便方法计算:123+234+345+456+567+678+789急
123+234+345+456+567+678+789
=（123+789）+（234+678）+（345+567）+456
=2X456+2X456+2X456+456
=7X456
=3192