推 ghkckhg :感謝~~ 04/18 00:47
※ 引述《ghkckhg (行人)》之銘言：
: 如圖:
: http://imageshack.us/photo/my-images/838/281464809999.jpg/
: 主要在於排組的部分解不出來，或是這題有什麼trick?
: 謝謝各位神手~
a 為下列程序的選法數:
將 30 個相異物選出至少三個物品裝進盒子裡, 再從盒子裡依序拿出三個物品
這等同於
將 30 個相異物中依序選出三個物品, 剩下的任意選擇要不要放進盒子裡
故 a = 30 * 29 * 28 * 2^27
取對數計算 (過程略) 可得到 log a 約為 12.多 故選 (B)
--
'You've sort of made up for it tonight,' said Harry. 'Getting the
sword. Finishing the Horcrux. Saving my life.'
'That makes me sound a lot cooler then I was,' Ron mumbled.
'Stuff like that always sounds cooler then it really was,' said
Harry. 'I've been trying to tell you that for years.'
-- Harry Potter and the Deathly Hollows, P.308
--
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