[閒聊] 開黃泉後盤面五屬珠都>=3顆的機率
看板ToS (神魔之塔(Tower of Saviors))作者znmkhxrw (QQ)時間8年前 (2017/09/09 23:32)推噓57(58推 1噓 37→)留言96則, 47人參與討論串1/3 (看更多)
大家好(‧^ω^‧)
剛剛狂日大大問了個 TOS-MATH 問題如題
正常關卡(非禁珠)下開黃泉洗珠,每一屬(不含心)都≧3顆的機率是?
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每一屬(不含心)都≧3顆的盤面
一開始採取正攻法,所求機率= ──────────────
6^30
【即每一格都有6種選擇(六色珠)】
但是分子靠杯難算,我試了:
(1) 假設至少某一色不到三個:
窮舉:水2
水1
水0
但是一旦開始窮舉火的時候,勢必會跟前面有重複地方,再來後面三屬重複越多
放棄!
(2) 先把每一屬都3個的格子先挑出來:C(30,15)
之後剩下15個格子都是6種選擇:6^15
結果就是 C(30,15)*6^15,但是這種也會有重複= = 放棄
再來換個方面想,反正盤面長相不重要,重要是珠子的個數而已
因此變成把30個格子分給6色:
令 x_1 為 水珠個數
x_2 為 火珠個數
x_3 為 木珠個數
x_4 為 光珠個數
x_5 為 暗珠個數
x_6 為 心珠個數
則 x_1+x_2+x_3+x_4+x_5+x_6=30 的非負整數解就是分母(不考慮排列)
x_1+x_2+x_3+x_4+x_5+x_6=15 的非負整數解就是分子(不考慮排列)
(會從30變成15是因為x_1~x_5都先各給了3格)
H(6,15) C(20,5)
因此機率 = ──── = ──── = 4.775%
H(6,30) C(35,5)
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到底是我算錯還是這空有假奶的女人有高於95%的機會解不了強化五屬盾 (._.?)
======================
EDIT:
算式錯誤 期誤會假奶 期待正解(‧^ω^‧)
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有道理耶 你這個例子至少一火會是3/4 但是 用H算會變成2/3
應該就是許老師說的機率不相等
※ 編輯: znmkhxrw (111.255.238.56), 09/09/2017 23:59:19
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※ 編輯: znmkhxrw (111.255.238.56), 09/10/2017 00:04:47
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