初中,有理数的加减法.(-7)-9-(-3)+(-5),-4.2+5.7-8.4+10,(-1.3)-(-3.2), -

(-7)-9-(-3)+(-5)
=-7-9+3-5
=-16-2
=-18;
-4.2+5.7-8.4+10
=-4.2-2.7+10
=-6.9+10
=3.1
(-1.3)-(-3.2)
=-1.3+3.2
=1.9
-1/4+5/6+2/3-1/2
=-1/4+5/6+4/6-2/4
=-3/4+9/6
=-3/4+3/2
=-3/4+6/4
=3/4