(2又1/7)-(-5又1/3)-(+3又1/7)-(-3又2/3)
=2又1/7+5又1/3+(-3又1/7)+3又2/3
=[2又1/7+(-3又1/7)]+(5又1/3+3又2/3)
=-(3又1/7-2又1/7)+9
=-1+9
=8
-15又1/3-(3又1/7)-4又2/3-(-8又1/7)
=-15又1/3+(-3又1/7)+(-4又2/3)+8又1/7
=[(-15又1/3)+(-4又2/3)]+(8又1/7-3又1/7)
=(-20)+5
=-15
-0.5-(3又1/4)+2.75-(7又1/2)
=-0.5+(-3.25)+2.75+(-7.5)
=2.75-(0.5+3.25+7.5)
=2.75-11.25
=-(11.25-2.75)
=-8.5