简便计算，各位哥哥姐姐急啊！！！！！

1.1/2+1/6+1/12+……+1/90
=(1-1/2)+(1/2-1/3)+……+(1/9-1/10)
=1-1/10
=9/10

2.1999÷1998/1999
=1999×1999/1998
=1999×(1998+1)/1998
=1999×1998/1998+1999*1/1998
=1999+1999/1998
=2000又1/1998

3.246×321963/123369
=246×321×1003÷(1003×123)
=321×2
=642

4.14.8×6.3+46.5×4.5+8.3×3.7+0.465×550-6.3×6.5
=6.3×（14.8－6.5）+46.5×（4.5+5.5）+8.3×3.7
=6.3×8.3+46.5×10+8.3×3.7
=8.3×(3.7+6.3)+465
=8.3×10+465
=83+465
=548

1. 1/2+1/6+1/12.......1/90=（1-1/2）+（1/2-1/3）+(1/3-1/4)......+(1/9-1/10)
=1-1/10
=9/10