Question

5个5加减乘除都要用怎样得4?可以用括号 必须加减乘除都要用到,不能重复!

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.
这个是百度上的答案