题目内容

7
8
+
4
5
-
1
5
+
1
8
=(
7
8
+
1
8
)-(
4
5
-
1
5
)
错误
错误
．
分析：根据加法交换律和加法结合律可计算
7
8
加
1
8
，然后再计算
4
5
减去
1
5
，最后再用
7
8
与
1
8
的和加上
4
5
与
1
5
的差结果不变．
解答：解：因为
7
8
+
4
5
-
1
5
+
1
8
=（
7
8
+
1
8
）+（
4
5
-
1
5
），
所以原题解答错误．
故答案为：错误．
点评：此题主要考查的是加法交换律和加法结合律的应用．
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直接写出得数．
4
5
-
1
5
=
1-
7
8
=
2
5
-
1
10
=
2
3
+
2
5
=
1
7
+
3
4
=
7
8
-
3
4
=		 1
2
5
+
3
5
=
1
16
+
1
4
=
1
4
-
3
9
=
5
8
-0.375=
（2007?东城区）
56-47= 10-0.27= 5-2.5= 6.3+0.7= 6÷0.5=
8.4÷4.2= 2.5×4= 1-
2
3
=
1
3
+
1
2
=
1
4
+
3
4
=
8
3
÷
8
3
=		 9÷10=
5
6
-
2
3
=
4
5
-
1
2
=
5
9
×18=
1
2
×
1
2
=
2
13
×2=		 0÷
5
6
=
8
9
÷4=
5
26
×13=
6÷
2
7
=		 12×
2
3
=
5
6
×
2
5
=
2
3
×
3
4
=
4
5
÷
1
5
=
1÷
1
8
=
4
7
×
7
8
=		 5÷
5
6
=
1
4
÷
1
3
=
6
7
÷
3
14
=
3×1.5= 2.5×4= 0÷0.9= 4÷0.2=
0.56÷0.7= 0.24×5= 0.2×5= 2.1-0.87=
3.54-3.5= 3.4-1.5= 12÷0.6= 8×0.125=
0.7×11= 0.13+1.7= 3.15÷0.5= 0.9÷4.5=
0.2×0.3= 1.2+0.56= 3-1.7= 1÷0.25=
78÷1.3= 15÷0.3= 2.1+1.49= 6.24-1.5=
1.2×0.3= 6.3÷6.3= 1.6×0.2= 3.7-1.2=
4.58-3.5= 72.8÷8= 3.5×0.3= 0.25×100=
3.2-2= 0.51÷17= 5.3÷0.01= 1.03×3=
2.8+12= 3.5×2= 2.2×0.1= 1-0.25=
0.62-0.32= 6.3÷0.21= 1.7×10= 0.12×3=
0.45×2= 1.2÷0.3= 1÷2= 4.8×100=
0.25×8= 0.89÷8.9= 17.8+2.2= 0.8÷0.2=
5.79÷0.1= 0.35+0.65= 8.9-0.9= 9.2-9.2=
3.6÷0.4= 15.15÷15= 0.2×0.3×0.1= 1.34×4×2.5=
3
8
×64=
2
5
×15=
2
7
×
3
4
=
9
16
×
2
3
=
16
21
×
7
8
=
45×
2
9
=		 1-
5
12
=
3
7
+
1
4
=
8
25
×
3
16
=
3
97
×97=
直接写出得数．
14÷35=
1
2
+
2
5
=
0.77+0.33=
4
5
×4+4×
1
4
=
1.4-0.6=
7
8
×
1
7
=
5-1.4-1.6= 2-
1
5
-
3
5
=

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