6 A random sample of 5 values of a variable \(X\) is given below.
$$\begin{array} { l l l l l }
2 & 3 & 3 & 5 & a
\end{array}$$
- Find an expression, in terms of \(a\), for the mean of these values.
It is given that an unbiased estimate of the population variance of \(X\), using these values, is 4 . It is also given that \(a\) is positive. - Find and simplify a quadratic equation in terms of \(a\) and hence find the value of \(a\).