Question

初中，有理数的加减法。-4.2+5.7-8.4+10，-1/4+5/6+2/3-1/2,12-（-18)+(-7)-15，4.7-（-8.9）-7.5+（-6）

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Answer 1

解：-4.2+5.7-8.4+10
=[(-4.2)+(-8.4)]+(5.7+10)
=(-12.6)+15.7
=15.7-12.6
=3.1

-1/4+5/6+2/3-1/2
=[(-1/4)+(-1/2)]+(5/6+2/3)
=(-3/4)+3/2
=3/2-3/4
=6/4-3/4
=3/4

12-(-18)+(-7)-15
=(12+18)+[(-7)+(-15)]
=30+(-22)
=30-22
=8

4.7-(-8.9)-7.5+(-6)
=(4.7+8.9)+[(-7.5)+(-6)]
=13.6+(-12.5)
=13.6-13.5
=0.1

Answer 2

解：[1]原式=-12.6+15.7=3.1
【2】原式=-3/4+9/6=-3/4+6/4=3/4
【3】原式=12+18-7-15=30-22=8
【4】原式=4.7+8.9-7.5-6=13.6-13.5=0.1

Answer 3

-4.2+5.7-8.4+10=1.5-8.4+10=3.1
1/4+5/6+2/3-1/2=（1/4-1/2)+(5/6+2/3)=(1/4-2/4)+(5/6+4/6)=-1/4+9/6=-1/4+6/4=5/4
12-（-18)+(-7)-15=12+18-7-15=8
4.7-（-8.9）-7.5+（-6）=4.7+8.9-7.5-6=0.1

Answer 4

1. =1.5-8.4+10
=-6.9+10
=3.1
2. =-3/12+10/12+8/12-6/12
=7/12+8/12-6/12
=15/12-6/12
=9/12
=3/4
3. =12+18-7-15
=30-7-15
=23-15
=8
4. =4.7+8.9-7.5-6
=13.6-7.5-6
=6.1-6
=0.1

Answer 5

3.1 0.75 8 13.6 -13.5