Q.

A die is rolled twice. Getting a number greater than 4 is called a ‘Success’. Let the random variable X is equal to the number of successes then mean of X is 
 

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a

34

b

23

c

13

d

14

answer is B.

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Detailed Solution

Let X be a radom variable of number of success.

 So, X can take values 0, 1, 2

 let 'S' denote the success of  getting 5 or 6

P(S)=P(5 or 6)=26=13      P(S)=1-13=23

Now P(x=0)=P(S·S)=23×23=49

         P(x=1)=P(S·S)+P(S·S)=49 P(x=2)=P(S·S)=13×13=19

Mean =0 49+1 49+2 19

           =69 =23

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