1、解:(1)5 +(-7)+ 8 -(5 + 8)+(-7)
= 13 +(-7) = 6
(2)(-1/3)+ 1/2 +(-2/3)
= [(-1/3)+(-2/3)] + 1/2
= (-1) + 1/2
= -1/2
(3)(-3.5)+[3 +(-1.5)] - [(-3.5)+(-1.5)] + 3
= (-5)+ 3
= 2
2、解:(1)(+14)+(-4)+(-1)+(+16)+(-5)
= [(+14)+(+16)]+[(-4)+(-1)+(-5)]
= 30 +(-10)
= 20
(2)(-18.65)+(-7.25)+(+18.15)+(+7.25)
= [(-18.65)+(+18.15)]+[(-7.25)+(+7.25)]
= (-0.5)+ 0
= 0.5
(3)(-2.25)+(-5/8)+(-3/4)+(+0.125)
= (-2.25)+(-0.625)+(-0.75)+(+0.125)
= [(-2.25)+(-0.75)]+[(-0.625)+(+0.125)]
=(-3)+(-0.5) = 3.5
理由略.
3、解:[(-2)+(-1)+(+2)+(+6)+(+4)+(+1)+(-3)] ÷ 7
= 7 ÷ 7 = 1(℃)。
答:这个星期的平均最低温度是1℃。