门|门CS 2012 |问题63

一家汽车厂从两家供应商X和Y那里购买减震器。X提供60%的减震器，Y提供40%的减震器。所有减震器都要经过质量测试。通过质量测试的产品被认为是可靠的。在X的减震器中，96%是可靠的。在Y的减震器中，72%是可靠的。

随机选择的可靠减震器由Y制成的概率为 （A） 0.288 （B） 0.334 （C） 0.667 （D） 0.720 答复: （B） 说明：

Probability that the absorber is reliable = 0.96*0.6 + 0.72*0.4 
                                          = 0.576 + 0.288


Probability that  the absorber is from y and reliable = 
            (Probability that is made by Y)  X (Probability that it is reliable)
           = 0.4 * 0.72 
           = 0.288

The probability that randomly picked reliable absorber is from y = 
    (Probability that  the absorber is from y and reliable) / (>Probability that the absorber is reliable )
   = (0.288)/ (0.576 + 0.288) 
   =  0.334 

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