第1个回答 2012-04-27
1.首项加末项乘以项数除以二
(5+100)*20/2=1050
2.(101+99)+(98+102)+(104+96)+103*2+98=806+98=904
3.71到98都约掉了
剩下99+100-70=129
4.(20-1)+(200-1)+(2000-1)+(20000-1)+(200000-1)=222220-5=222215
5.同上一题:222...220(1999个)-1999=222...2220221(1996个)
6.同上一题:(1000000-100000-2)+(100000-10000-2)+(10000-1000-2)+(1000-100-2)+(100-10-2)
=1000000-2-2-2-2-10-2
=999980
7.(400000-1)+(40000-1)(4000-1)+(400-1)+(40-1)+(4-1)
=444444-6
=444438
8.同第一题:(1+78)*78/2=3081
9.同上一题:5000-(1+90)*90/2=905
10.(25+26+27+28+29+30)-(12+13+14+15+16+17)
=27.5*6-14.5*6
=165-87
=78
11.是不是打错了漏了5,从4直接到了6
12.不会,回家想一想
13.1+2+3+4=10
所以,原式=11110
14.同上一题:5+6+7+8+9=35
所以:原式=350000+35000+3500+350+35=388885
15.前面2*499+9001-499500=489998
16.4个一组,每组等于4
所以:原式=1994/4*4=1994
17.同上一题:4个一组,每组等于8
所以:原式=1996/4*8=3992
18.把式子上的-1997改成+1997,末尾再减去3994。
这样就同上一题了。6个一组,每组等于9
第2个回答 2012-03-18
1.8*100+45+100=945
2.
第3个回答 2009-07-13
第一题:(5+100)×[(100-5)/5+1]/2
=105×20/2
=1050
第4个回答 2009-07-13
1. =(5+100)100×9+3-1+3-4+2+4-2-2+1=904(100÷5)÷2
=105×20÷2
=1050
2. =100×9+3-1+3-4+2+4-2-2+1=904
3. =99+100-70
=129
4. =20+200+2000+20000+200000-5
=222220-5
=222215
5. =22222(1998个2)0-1999
6. =90+900+9000+90000+900000-(5×2)
=999990-10
=999980
7. =400000+40000+4000+400+40+4-(1×6)
=444444-6
=444438
8. =(1+78)×78÷2
=79×78÷2
=3081
9. =5000-(1+2+3+....+90)
=5000-(91×90÷2)
=5000-4095
=905
10.=(25+26+27+28+29+30)-(12+13+14+15+16+17)
=[(25+30)×6÷2]-[(12+17)×6÷2]
=(55×6÷2)-(29×6÷2)
=78
11.
第5个回答 2009-07-16
.首项加末项乘以项数除以二
(5+100)*20/2=1050
2.(101+99)+(98+102)+(104+96)+103*2+98=806+98=904
3.71到98都约掉了
剩下99+100-70=129
4.(20-1)+(200-1)+(2000-1)+(20000-1)+(200000-1)=222220-5=222215
5.同上一题:222...220(1999个)-1999=222...2220221(1996个)
6.同上一题:(1000000-100000-2)+(100000-10000-2)+(10000-1000-2)+(1000-100-2)+(100-10-2)
=1000000-2-2-2-2-10-2
=999980
7.(400000-1)+(40000-1)(4000-1)+(400-1)+(40-1)+(4-1)
=444444-6
=444438
8.同第一题:(1+78)*78/2=3081
9.同上一题:5000-(1+90)*90/2=905
10.(25+26+27+28+29+30)-(12+13+14+15+16+17)
=27.5*6-14.5*6
=165-87
=78
11.是不是打错了漏了5,从4直接到了6
12.不会,回家想一想
13.1+2+3+4=10
所以,原式=11110
14.同上一题:5+6+7+8+9=35
所以:原式=350000+35000+3500+350+35=388885
15.前面2*499+9001-499500=489998
16.4个一组,每组等于4
所以:原式=1994/4*4=1994
17.同上一题:4个一组,每组等于8
所以:原式=1996/4*8=3992
18.把式子上的-1997改成+1997,末尾再减去3994。
这样就同上一题了。6个一组,每组等于9