A four-character password consists of one letter of the alphabet and three different digits between 0 and 9,inclusive.The letter must appear as the second or third character of the password.How many different passwords are possible?答案是37440?

A four-character password consists of one letter of the alphabet and three different digits between 0 and 9,inclusive.The letter must appear as the second or third character of the password.How many different passwords are possible?
答案是37440?

对
A(下标10上标3）*26*2=37440
A代表：10个数字（0-9）被随便排在除了字母那位剩下的三位中
26代表：字母的可能性（一共26个字母）
2代表：两种可能性——字母可出现在第二位/第三位上