问题 解答题
5
8
+
7
9
+
3
8

25
18
-
2
5
-
3
5

2
3
+
7
10
+
1
3
+
3
10

5
9
-
5
12
+
4
9

8
9
-(
1
5
-
1
9
)

5
12
+
11
15
-
6
15
+
7
12
答案

(1)

5
8
+
7
9
+
3
8

=(

5
8
+
3
8
)+
7
9

=1+

7
9

=1

7
9

(2)

25
18
-
2
5
-
3
5

=

25
18
-(
2
5
+
3
5
),

=

25
18
-1,

=

7
18

(3)

2
3
+
7
10
+
1
3
+
3
10

=(

2
3
+
1
3
)+(
7
10
+
3
10
),

=1+1,

=2;

(4)

5
9
-
5
12
+
4
9

=(

5
9
+
4
9
)-
5
12

=1-

5
12

=

7
12

(5)

8
9
-(
1
5
-
1
9
),

=

8
9
-
1
5
+
1
9

=(

8
9
+
1
9
)-
1
5

=1-

1
5

=

4
5

(6)

5
12
+
11
15
-
6
15
+
7
12

=(

5
12
+
7
12
)+(
11
15
-
6
15
),

=1+

1
3

=1

1
3

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