(+1/2)-[(-2) +( 1/2)]
=1/2-(-2+1/2)
=1/2+2-1/2
=2
-3-4+19-11+2
=-3-4+8+2
=-7+10
=3
-4.2+5.7-7.6+10.1-5.5
=1.5-7.6+10.1-5.5
=-4-7.6+10.1
=-1.5
（-52）+（-19）-（+37）-（-24）
=-52-19-37+24
=-(52+19+37)+24
=-84
13-[26-（-21）+（-18）]
=13-(26+21-18)
=13-29
=-16
丨-9/4丨-（-3/4）+1-丨1-1/2丨
=9/4+3/4+1-1/2
=3+1-1/2
=7/2