1.To keep computer files secure,many programs require the user to enter a password.The shortest allowable passwords are typically six characters long and can contain both numbers and letters .How many six-character passwords are possible if (a)characters can be repeated and (b) characters cannot be repeated?
问题描述：
1.To keep computer files secure,many programs require the user to enter a password.The shortest allowable passwords are typically six characters long and can contain both numbers and letters .How many six-character passwords are possible if (a)characters can be repeated and (b) characters cannot be repeated?
答
就是密码最少是6位数的数字或者字母组成,1,当数字或者字母可以重复的时候,密码能有多少个?2.当不可以重复使用的时候能有多少个