初一的有理数的加减混合运算

1.
原式=33.1+22.9-10.5
=56-10.5
=45.5
2.
原式=-8+15-9+12
=7-9+12
=-2+12
=10
3.
原式=-2/3-1/6+1/4-1/2
=（-2*4-2+3-6）/12
=(-8-2+3-6)/12
=-13/12
4.
原式=3/5-3/2-11/4+13/4
=(3*4-3*10-11*5+13*5)/20
=(12-30-55+65)/20
=(-18+10)/20
=-8/20
=-2/5