查人人中国名人网en1090 2:几道简单的题目
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观察特点，再计算{请把答案写清楚}
1， 1 2 1999
这些是分数: ----- + ------ + … + ------ =怎麽计算?
1999 1999 1999
2, 1 1 1 1 2 3 4 1998
(--- + --- + --- + … + -----)+(--- + --- + --- + … + -----)
3 4 5 1999 3 4 5 1999
||英语||
排序号.
( )1.How do you help at the home ,then?
( )2.But I never water the plants.
( )3.Do you always sweep at the home?
( )4.My mother does.
( )5.You are so helpful at the home.
( )6.Who usually water the plants?
( )7.Hello,Lily.What are you doing now?
( )8.I usually wash the dishes.I sometimes clean the room.
( )9.Yes,of course.I like sweeping.
( )10.I'm sweeping the floor.
1， 1 2 1999
这些是分数: ----- + ------ + … + ------ =怎麽计算?
1999 1999 1999
2, 1 1 1 1 2 3 4 1998
(--- + --- + --- + … + -----)+(--- + --- + --- + … + -----)
3 4 5 1999 3 4 5 1999
||英语||
排序号.
( )1.How do you help at the home ,then?
( )2.But I never water the plants.
( )3.Do you always sweep at the home?
( )4.My mother does.
( )5.You are so helpful at the home.
( )6.Who usually water the plants?
( )7.Hello,Lily.What are you doing now?
( )8.I usually wash the dishes.I sometimes clean the room.
( )9.Yes,of course.I like sweeping.
( )10.I'm sweeping the floor.
1. 1/1999 + 2/1999 + ... + 1999/1999
=(1+2+3+4+...+1998+1999)/1999
=[(1+1999)*1999/2]/1999
=1000
2.运用加法交换律和分配律
= (1/3+2/3)+(1/4+3/4)+(1/5+4/5)+(1/1999+1998/1999)
= 1 + 1 + 1 +1
=4
英语排序号：
7 10 3 9 5 1 8 6 4 2
7-10-3-9-5-1-8-6-4-2
1. 1/1999 + 2/1999 + ... + 1999/1999
=(1+2+3+4+...+1998+1999)/1999
=[(1+1999)*1999/2]/1999
=1000
2.运用加法交换律和分配律
= (1/3+2/3)+(1/4+3/4)+(1/5+4/5)+……+(1/1999+1998/1999)
= 1 + 1 + 1+…… +1 （1999个）
=1999
英语排序号：
7 10 3 9 5 1 8 6 4 2
1000
1999
7 10 3 9 5 1 8 6 4 2