Help ! ! ! 3條好難的Maths 題目!

(1)
設＄x 為貨物的價錢
　現共需付:
x+x+0.4*x
=$2.4x
每件貨物比原價節省
=(3x-2.4x)/3x *100%
=20%

(2) 2*999+998*999
=(2+998)*999
=1000*999
=999000

2007-06-02 16:04:48 補充：
(3) 11+12+13+14...+50 =(1+2+3+...+50)-(1+2+3...+10) =(1+50)*50/2 - (1+10)*10/2 =1275 - 55 =1220 22+24+26+...+100 =(11+12+13+...+50)*2 =1220*2 =2440

2007-06-03 17:57:00 補充：
(3) 11 12 13 14......... 50 --------------------------------------------- = 22 24 26 ................ 100 11 12 13 14......... 50 = --------------------------------------------- 2*(11 12 13 14......... 50) 1 ------ 2

2007-06-07 15:47:24 補充：
333*111 =3*111*111=3*12321=36963

(3) 11+12+13+14.........+50
--------------------------------------------- =???
22+24+26+................+100

分子項數 = 50+1-11= 40
分母項數 = 100+1-22 = 79

[(頭項+尾項) X 項數]/2

--------------------------------------------- =???
[(頭項+尾項) X 項數]/2

[(11+50) X 40]/2

--------------------------------------------- =0.253
[(22+100) X 79]/2

2007-06-02 16:19:36 補充：
sorry,我計錯分母，上面的那位對的。