10 apples, 4 of which are rotten, are in the refrigerator. 3 apples are randomly selected without replacement. Let the random variable x represent the number chosen that are rotten. What is the mean and standard deviation of x?

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Answer 1 · 2015-10-23T11:18:31

x: 0 1 2 3
P(x): 6c3/10c3 ; (6c24c1)/10c3 ; (6c14c2)/10c3 ; 4c3/10c3
= 0.17 ; 0.5 ; 0.3 ; 0.03

mean = 00.17 + 10.5 +20.3 +30.03
= 1.19 (Ans.)