今天又是有大陆地区GRE线下考试的日子～
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今日最新考题
Passwords for a certain computer consist of 5 symbols typed on a computer keyboard. Each password consists of one @ symbol two # symbols, and two $ symbols, typed in any order. For example, @#$$# and $#$#@ are two different passwords for the computer.
Quantity A
The total number of different passwords for the computer
Quantity B
30
答案
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解题思路
考点：排列组合 去重公式
