几道数学计算题,

题目

几道数学计算题,
计算（要写过程）
(-1/3)+(+1/2)+(-2/3)+(+4/5)+(-1/2)
(+13又1/23)+(-55又1/33)+(+7又21/46)+(-14又5/60)
(+0.75)+(-1又7/120)
(+5/8)+(-0.675)
2+(-4)+6(-8)+...+18+(-20)
1+2+3+...1997+1998+1999
(-2/3)-(+1/6)-(-1/4)-(+1/2)
(-4又5/6)-(+3又3/5)-(-3又1/6)-(+1又1/5)

答案

(-1/3)+(+1/2)+(-2/3)+(+4/5)+(-1/2) =-1/3+1/2-2/3+4/5-1/2=-1/3-2/3+4/5=-1+4/5=-1/5 (+13又1/23)+(-55又1/33)+(+7又21/46)+(-14 又5/60) =13 1/23-55 1/33+7 21/46-14 5/60=1又17/44 (+0.75)+(-1又7/120)=0.75-1 ...