From the numbers 3,5,5,7,7,7,9,9,9,9 one number is selected . . .

Question : From the numbers 3,5,5,7,7,7,9,9,9,9 one number is selected at random. The probability that the selected number is mean of the data is given by 
a) 1/10

b) 3/10

c) 7/10

d) 9/10 

Doubt by Saksham

Solution : 

3,5,5,7,7,7,9,9,9,9 

Mean (X̄)
= Sum of observations / Total number of observations

= (3+5+5+7+7+7+9+9+9+9)/10

= (3+10+21+36)/10
= 70/10

= 7

P(E) = No. of favorable outcomes / Total Number of possible outcomes

P(Selected Number is a Mean) = 3/10 = 0.3

Hence, b) 3/10, would be the correct option.