✔ 最佳答案
假設現在有27個藍色波,37個黃色波,36個紅色波,n=100。現在random地抽 5個波 at a time with replacement.
= = = = =
(1)
B = blue ball
N = not blue ball
由於有 replacement,每次都係由 100 balls 抽出 1 ball。每一次:
P(B) = 27/100
P(N) = 1 - (27/100) = 73/100
P(at most 2 B)
= P(0B5N) + P(1B4N) + P(2B3N)
= (73/100)^5 + 5C1*(27/100)*(73/100)^4 + 5C2*(27/100)^2*(73/100)^3
= 4371384029/5000000000 or 0.8742768058
= = = = =
(2)
P([at most 2B] and [at least 2N])
= P([at most 2B] and [at most 3B])
= P(at most 2B)
= 0.8742768058
P(at least 2N)
= P(0B5N) + P(1B4N) + P(2B3N) + P(3B2N)
= 0.8742768058 + 5C3*(27/100)^3*(73/100)^2
= 0.9791675128
P(at most 2B | at least 2N)
= P([at most 2B] and [at least 2N]) / P(at least 2N)
= 0.8742768058/0.9791675128
= 820301/918716 or 0.8928776684