快!!!!!

1) 1+2+3+....+1000=(1+1000)(1000)/2 = 500500

2) Since for terms larger than 5, the last digit must be zero (eg: 2 x 5 = 10)
So we need to consider the first 4 terms only.

1 + 2 + 6 + 24 + .... (Starting from term 5, all end with zero)

The last digit is 3.

3) 1+2-3+4-5+....-1997+1998
= -1-2-3-4-5-...-1997-1998 + 2+ 2(2+4+6+8+...+1998)
= (-1-1998)(1998)/2 + 2 +2(2+1998)(1998/2)/2
=-1997001+2+1998000
=1001

or

since 2-3 = -1, 4-5=-1 ....
then

the first and last number is not count the number of -1 is (1998-2)/2=998

1-998+1998=1001

1) 1+2+3+4+................+1000= ?

1+2+3+4+................+1000=
500500

1)
1+2+3+4+.................................+1000
=(1+1000)x1000/2
=1001x1000/2
=500500
2)
1+(1*2)+(1*2*3)+..........(1*2*3.....*100)的個位數字是3
3)
1+2-3+4-5+6..........-1997+1998
=1001

2007-07-03 16:54:14 補充：
2)因為1*2*3*4*5=120,0*?=?0,所以只要計1+(1*2)+(1*2*3)+(1*2*3*4)讛就行

1.(1+1000)*1000/2=500500