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NCERT Class XII Mathematics Chapter - - Solutions

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Question : 66
Total: 101
The mean of the numbers obtained on throwing a die having written 1 on three faces, 2 on two faces and 5 on one face is
Solution:  
X denote the random variable, which represents the number obtain on throwing a die
∴ X can assume values 1, 2 and 5.
P(X = 1) = P(getting 1) =
3
6
=
1
2
; P(X = 2) = P (getting 2) =
2
6
=
1
3

P(X = 5) = P (getting 5) =
1
6

Hence, the probability distribution is :
 X  1  2  5
 P(X)  
1
2
  
1
3
  
1
6
∴ Mean =E(X)=∑XP(X) =1×
1
2
+2×
1
3
+5×
1
6
=2
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