推 AmigoSafin : 感謝幫忙~~ 09/21 00:18
※ 引述《AmigoSafin ()》之銘言:
: 大家好~
: 不好意思我當時在做這個題目時
: 真心覺得是簡單的題目
: 但是被改出來卻沒有拿到半點分數@@
: 加上老師奇怪的堅持不公佈答案
: 我只好po上自己的答案並來向大家請益
: 題目是英文 但很好理解的
: 先謝謝大家了
: A manufacturing plant has 3 different machines denoted M1, M2 and M3; 20%,
: 35% and 45% of the production comes from machines M1, M2 and M3,
: respectively; 3% of the production from M1 is defective, 2% of the production
: from M2 is defective and 1% of the production from M3 is defective, all at
: random.
: a. Calculate the percent of defective items from the entire manufacturing
: plant.
: b. A truck load of items is brought to a quality control clerk who randomly
: selects one item and finds it to be defective. What is the probability that
: this item was manufactured by machine M2?
: 我的答案是
: a.1.8% (0.018)
有點小差距(?
0.2*0.03+0.35*0.02+0.45*0.01=0.0175
: b.0.02 (2%)
條件機率
M2壞/全部壞
(0.35*0.02)/0.0175=0.4
: 我的想法就是設定全部products是S
: M1 0.20S
: M2 0.35S
: M3 0.45S
: 而其中有缺陷的 就用M1:0.2S^(缺陷的比例)
: 所以a小題的答案我就會用所有的有缺陷的比例去除以S
: 這樣做錯了嗎?
: 老實說很訝異我沒有拿到這題分數:(
: 請大家不吝指點小魯~
: 謝謝!
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※ 編輯: CalcuLouis (140.113.90.60), 09/20/2018 13:40:59