4/5+(7/8−4/5) 7/10−(2/15+1/6) 1−1/3−1/7.

问题描述:

4
5
+(
7
8
4
5
)
7
10
−(
2
15
+
1
6
)

1−
1
3
1
7

(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