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PROBABILITY

1. ACCORDING TO STATISTICAL DEFINITION OF PROBABILITY P(A) = lim FA/n WHERE FA IS THE NUMBER OF TIMES EVENT A OCCUR AND n IS THE NUMBER OF TIMES THE EXPERIMANT IS REPEATED.

2. IF P(A) = 0, A IS KNOWN TO BE AN IMPOSSIBLE EVENT AND IS P(A) = 1, A IS KNOWN TO BE A SURE EVENT.

3. BINOMIAL DISTRIBUTIONS IS BIPARAMETRIC DISTRIBUTION, WHERE AS POISSION DISTRIBUTION IS UNIPARAMETRIC ONE.

4. THE CONDITIONS FOR THE POISSION MODEL ARE :

• THE PROBABILIY OF SUCCESS IN A VERY SMALL INTERAVAL IS CONSTANT.

• THE PROBABILITY OF HAVING MORE THAN ONE SUCCESS IN THE ABOVE REFERRED SMALL TIME INTERVAL IS VERY LOW.

• THE PROBABILITY OF SUCCESS IS INDEPENDENT OF t FOR THE TIME INTERVAL(t ,t+dt) .

5. Expected Value or Mathematical Expectation of a random variable may be defined as the sum of the products of the different values taken by the random variable and the corresponding probabilities. Hence if a random variable X takes n values X1, X2,………… Xn with corresponding probabilities p1, p2, p3, ………. pn, then expected value of X is given by µ = E (x) = Σ pi xi .

Expected value of X2 is given by E ( X2 ) = Σ pi xi2

Variance of x, is given by σ2 = E(x- µ)2 = E(x2)- µ2

Expectation of a constant k is k

i.e. E(k) = k fo any constant k.

Expectation of sum of two random variables is the sum of their expectations

i.e. E(x +y) = E(x) + E(y) for any two random variable x and y

Expectation of the product of a constant and a random variable is the product of the constant and the expectation of the random variable.

i.e. E(k x) = k.E(x) for any constant k

Expectation of the product of two random variable is the product of the

i.e. E(xy) = E(x) . E(y)

Whenever x and y are independent.

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