求2道计算题,一：9+99+999+9999 二：998+997+996+1002+1003+1004 = = = =

9+99+999+9999
=1+9+1+99+1+999+1+9999-4
=11110-4
=11106
二：
998+997+996+1002+1003+1004
=(998+1002)+(997+1003)+(996+1004)
=2000+2000+2000
=6000