练习(P31)
1.(1)(+3)+(-13)+(+7)=(+3)+(+7)+(-13)=[(+3)+( +7)]+(-13)=(+10)+(-13)
= -3.
(2)(+0.56)+(-0.9)+(+0.44)+(-8.1)=[(+0.56)+(+0.44)]+[(-0.9)+(-8.1)]=(+1)+( -9)= -8.
2.(+0.5)+(+0.3)+(-0.2)+0+(+0.2)+(-0.5)+0+(+0.2)+(-0.3)+(-0.1)=0.1(kg).10x10+0.1=100.1(kg).答:这10箱苹果的总质量是100.1kg