999*111＋333*667=999*111+333*(666+1)=999*111+333*666+333=333*(3+1*2+1)=333*6=1998123+234+345+456+567+678+789 =123*7+111*(1+2+3+4+5+6)=123*7+111*21=3192或123+234+345+456+567+678+789==(100+700)*(7/2)+(2...