题目

5个5加减乘除各用一次怎么等于4可以用括号

提问时间：2020-08-10

答案

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.