(-1997)+1又2/3+1995+(-2又1/3)+(-1997)-(-2/3)+1
= -1997-1997+1995+1又2/3-2又1/3+2/3+1
= -1999+1
= -1998
（+11）+（-1/2）+（+7）+（-1/6）+（+2）+（-1/3）
=11-1/2+7-1/6+2-1/3
=11+7+2-3/6-1/6-2/6
=20-1
=19
(-1/2)-(-2又1/3)+2又3/4+(-7/8)-3又2/3
= -1/2+2又1/3+2又3/4-7/8-3又2/3
= -2/4+2又3/4-7/8+2又1/3-3又2/3
=11/8-4/3
=33/24-32/24
=1/24