一、计算
1.123+234+345+456+567+678+789
=100+200+300+400+500+600+700+20+30+40+50+60+70+80+3+4+5+6+7+8+9
=400*7+50*7+6*7
=456*7
=2492
2.2998/(2998+2998/2999)+1/3000
=2998/[(2998*2999+2998)/2999]+1/3000
=2998/[2998*3000/2999]+1/3000
=2999/3000+1/3000
=1
3.2003/(2003+2003/2005)+1/2006
=2003/(2003*2006/2005)+1/2006
=2005/2006+1/2006
=1
4.看不太懂
二、判断
解1.错2.错
三、应用(抱歉时间不足,略掉)