Answer :

X represents the number of black balls drawn.

X can take values 0,1 and 2

there are total 7 balls

n(S) = total possible ways of selecting 2 balls =

P(X=0) = P(selecting no black balls) =

P(X=1) = P(selecting 1 black ball and 1 red ball)


P(X=2) = P(selecting 2 black ball and 0 red ball) =

X is said to be a random variable if some of the probabilities associated with each value of X is 1


P(X=0) + P(X=1) + P(X=2) =

X is a random variable.

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 representing probability distribution gives the required products :

Mean =

Variance = ∑ xi2pi – (∑xipi)2

Variance =

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