Question

急!!!! 5个4怎么等于5

Answer 1

4种运算各用1次，所以任何2个5之间都必须填上1个运算符，不会出现55，555的情况。
按照实际计算的顺序，【相当于计算机计算时的顺序，也就是去掉括号后的计算顺序】，4个运算符只有4！=
4*3*2*1
=
24种。
因此，
5个5加减乘除各用1次，至多只有24个不同的结果。
下面列出这24种情形，
5+5
=
10,
10
-
5
=
5,
5*5
=
25,
25/5
=
5
[+-*/]
5+5
=
10,
10
-
5
=
5,
5/5
=
1,
1*5
=
5
[+-/*]
5+5
=
10,
10*5
=
50,
50-5
=
45,
45/5
=
9
[+*-/]
5+5
=
10,
10*5
=
50,
50/5
=
10,
10-5
=
5
[+*/-]
5+5
=
10,
10/5
=
2,
2-5
=
-8,
-8*5
=
-40
[+/-*]
5+5
=
10,
10/5
=
2,
2*5
=
10,
10
-
5
=
5
[+/*-]
5
-
5
=
0,
0
+
5
=
5,
5*5
=
25,
25/5
=
5
[-+*/]
5
-
5
=
0,
0
+
5
=
5,
5/5
=
1,
1*5
=
5
[-+/*]
5
-
5
=
0,
0*5
=
0,
0
+
5
=
5,
5/5
=
1
[-*+/]
5
-
5
=
0,
0*5
=
0,
0/5
=
0,
0
+
5
=
5
[-*/+]
5
-
5
=
0,
0/5
=
0,
0
+
5
=
5,
5*5
=
25
[-/+*]
5
-
5
=
0,
0/5
=
0,
0*5
=
0,
0
+
5
=
5
[-/*+]
5*5
=
25,
25+5
=
30,
30-5
=
25,
25/5
=
5
[*+-/]
5*5
=
25,
25+5
=
30,
30/5
=
6,
6
-
5
=
1
[*+/-]
5*5
=
25,
25-5
=
20,
20+5
=
25,
25/5
=
5
[*-+/]
5*5
=
25,
25-5
=
20,
20/5
=
4,
4
+
5
=
9
[*-/+]
5*5
=
25,
25/5
=
5,
5
+
5
=
10,
10-5
=
5
[*/+-]
5*5
=
25,
25/5
=
5,
5-5
=
0,
0
+
5
=
5
[*/-+]
5/5
=
1,
1+5
=
6,
6
-
5
=
1,
1*5
=
5
[/+-*]
5/5
=
1,
1+5
=
6,
6*5
=
30,
30
-
5
=
25
[/+*-]
5/5
=
1,
1-5
=
-4,
-4+5
=
1,
1*5
=
5
[/-+*]
5/5
=
1,
1-5
=
-4,
-4*5
=-20,-20+5
=
-15
[/-*+]
5/5
=
1,
1*5
=
5,
5
+
5
=
10,
10
-
5
=
5
[/*+-]
5/5
=
1,
1*5
=
5,
5
-
5
=
0,
0
+
5
=
5
[/*-+]
因为上面24个结果中没有4，
所以，
5个5加减乘除各用一次怎么也不可能等于4。