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{\bf Question}
Suppose that $40\%$ of the students in a large population are
freshman, $30\%$ are sophomores, $20\%$ are juniors and $10\%$ are
seniors. Suppose that 10 students are selected at random from te
population; and let $X_1,X_2,X_3,X_4$ denote, respectively, the
numbers of freshmen, sophomores, juniors, and seniors that are
obtained.
\begin{description}
\item[(a)]
Determine $\rho(X_i,X_j)$ for each pair of values $i$ and $j\
(i