[问题] GRE一题机率(应该吧XD)求教

楼主: AmigoSafin   2017-10-23 21:25:24
From the set of 6 letter of A, B, C, D, E, F,
there are 20 different 3-letter subsets that could be selected.
Quantity A: The number of 3-letter subsets that include the letter F
Quantity B: 10
1) A > B
2) A < B
3) A = B
4) The relationship cannot be determined from the information given
答案是3
如果有板有有时间的话,还请给小的一点指点~感恩~
作者: onlythecomet (柏)   2017-10-23 21:43:00
三个里面F固定一个,剩下两个位置C5取2=10

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