Statistics 問題(20 points)

2009-11-21 5:25 pm

求教及步驟問題如下

packs ball in a box of 30 ,the balls are expected to meet a specification on spherical shape. suppose that due to some fault during the production process,eatch of the boxes that were packed last week contains nine ball that do not meet the shape specification. without any knowledge of the incident,a quality control inspector has randomly selected abox that was packed last week ,and six balls will randomly be selected from the box for a thorrough examination of their spherical shape.

find the probability that among the six balls selected ,three of them do not meet the shape specification if

1.the slection of balls from the box with replacement

2. the slection of balls from the box without replacement

回答 (1)

用戶9112

2009-11-21 6:03 pm

✔ 最佳答案

(1) The probability of drawing one out of specification ball = 9/30 = 3/10
Probability that 3 balls not meeting specification = 6C3 * (3/10)^3 * (7/10)^3
= 0.1852
(2) Probability that 3 balls are out of spec without replacement = 6C3 * (9/30)(8/29)(7/28)(21/27)(20/26)(19/25)
= 0.1882

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