问题 解答题
用简便方法计算.
5-
3
7
-
4
7
1
6
+
3
8
+
5
8
5
9
-(
5
6
-
7
12
)
11
12
+
5
8
+
1
8
+
1
12
7
9
-(
1
3
+
4
9
3
20
+
8
15
+
17
20
答案

(1)5-

3
7
-
4
7

=5-(

3
7
+
4
7
),

=5-1,

=4;

(2)

1
6
+
3
8
+
5
8

=

1
6
+(
3
8
+
5
8
),

=

1
6
+1,

=1

1
6

(3)

5
9
-(
5
6
-
7
12

=

5
9
-
1
4

=

11
36

(4)

11
12
+
5
8
+
1
8
1
12

=(

11
12
+
1
12
)+(
5
8
+
1
8

=1+

3
4

=1

3
4

(5)

7
9
-(
1
3
+
4
9

=-

7
9
-
4
9
-
1
3

=

1
3
-
1
3

=0;

(6)

3
20
+
8
15
+
17
20

=

3
20
+
17
20
+
8
15

=1+

8
15

=1

8
15

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