※ 引述《yyiitt1003 (小眼鋼牙妹)》之銘言：
: GWD22 Q11
: In a stack of cards, 9 cards are blue and the rest are red. If 2 cards are to be chosen at random from the stack without replacement,
: the probability that the cards chosen will both be blue is 6/11.What is the number of cards in the stack?
: A.10 B.11 C.12 D.15 E.18
一共有N個球
則 藍球的次數 C9取2 (9*8)/2 6
-------------- = ------------ = -------------- = ----
全部的次數 CN取2 (N)(N-1)/2 11
解得 N = 12
--
※ 發信站: 批踢踢實業坊(ptt.cc)
◆ From: 118.169.192.103