(+3/4)-(+8)+(2又1/3)-(+3又1/4)-(-1又2/3)
=3/4-8+2又1/3-3又1/4+1又2/3
=(3/4-3又1/4)-8+(2又1/3+1又2/3)
=-2又1/2-8+4
=-6又1/2