(+6又3/5)+(-5又2/3)+(+4又2/5)+(+2又1/7)+(-1)+(-1又1/7)
=(+6又3/5) +(+4又2/5)+(+2又1/7)+(-1)+(-1又1/7)+(-5又2/3)
=[(+6又3/5) +(+4又2/5)]+[(+2又1/7)+(-1)+(-1又1/7)]+(-5又2/3)
=11+0+(-5又2/3)
=5又1/3