A fair die is tossed. Let X denote twice the number appearing. Find probability distribution, mean and variance of X.

When a fair dice is thrown there are total 6 possible outcomes.


X denote twice the number appearing on die


X can take values 2,4,6,8,10 and 12


As appearance of a number on a fair die is equally likely


i.e. P(appearing of 1) = P(appearing of 2) = P(appearing of 3) = P(appearing of 4) = P(appearing of 5) = P(appearing of 6) = 1/6


appearance of twice of the number is also equally likely with a probability of 1/6.


P(X=2)=P(X=4)=P(X=6)=P(X=8)=P(X=10)=P(X=12)=1/6


Now we have pi and xi.


Let’s proceed to find mean and variance.


Mean of any probability distribution is given by Mean = ∑xipi


Variance is given by:


Variance = ∑ xi2pi – (∑xipi)2


first we need to find the products i.e. pixi and pixi2 and add them to get mean and apply the above formula to get the variance.


Following table gives the required products :


Required Probability distribution table:-



Mean =


Variance =


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