问题 解答题
4
5
+(
7
8
-
4
5
)

7
10
-(
2
15
+
1
6
)

1-
1
3
-
1
7
答案

(1)

4
5
+(
7
8
-
4
5
),

=

4
5
+
7
8
-
4
5

=

4
5
-
4
5
+
7
8

=

7
8

(2)

7
10
-(
2
15
+
1
6
),

=

7
10
-
3
10

=

2
5

(3)1-

1
3
-
1
7

=1-

7
21
-
3
21

=

11
21

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