问题 解答题
用简便方法计算下列各题:
11
12
+
5
8
+
3
8
+
1
12
          ②5-
3
7
-
4
7
           ③
2
5
×20+
3
5
×20.
答案

11
12
+
5
8
+
3
8
+
1
12
  

=(

5
8
+
3
8
)+(
11
12
+
1
12
),

=1+1,

=2;

②5-

3
7
-
4
7

=5-(

3
7
+
4
7
),

=5-1,

=4;

2
5
×20+
3
5
×20

=(

2
5
+
3
5
)×20,

=1×20,

=20.

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