解:(1)(-8)+10+2+(-1)
=(10+2)+[(-8)+(-1)]
=12+(-9)
=3;
(2)5+(-6)+3+9+(-4)+(-7)
=(5+3+9)+[(-6)+(-4)+(-7)]
=17+(-17)
=0;
(3)(-0.8)+1.2+(-0.7)+(-2.1)+0.8+3.5
=(1.2+0.8+3.5)+[(-0.8)+(-0.7)+(-2.1)]
=5.5+(-3.6)
=1.9;
或:原式=[(-0.8)+0.8]+(1.2+3.5)+[(-0.7)+(-2.0)]
=0+4.7+(-2.8)
=1.9;
(4)
;
。
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