Question
Two numbers are selected at random (without replacement) from first six positive integers. Let X denote the larger of the two numbers obtained. Find the probability distribution of X. Find the mean and variance of this distribution.

Answer

$\text{x}:$ 2 3 4 5 6
$\text{P(x):}$ $\frac{1}{15}$ $\frac{2}{15}$ $\frac{3}{15}$ $\frac{4}{15}$ $\frac{5}{15}$
$\text{x.P(x):}$ $\frac{2}{15}$ $\frac{6}{15}$ $\frac{12}{15}$ $\frac{20}{15}$ $\frac{30}{15}$
$\text{x}^{2}\text{P(x):}$ $\frac{4}{15}$ $\frac{18}{15}$ $\frac{48}{15}$ $\frac{100}{15}$ $\frac{80}{15}$
$\text{Mean} = \sum \text{x. P(x)} = \frac{70}{15}=\frac{14}{3}$
$\text{Variance} = \sum \text{x}^{2}\text{p(x) = (Mean)}^{2} = \frac{350}{15}-\frac{196}{9} = \frac{14}{9} $

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