Show that when $\Psi(x, l)=\Sigma a_{n} \Psi_{n}(x, t),(E)=\Sigma a_{n}^{*} a_{n} E_{n}$ and thus that
$a_{n}^{*} a_{n}$ is the probability of obtaining the value $E_{n}$ as the result of a single measurement of the total energy $E$ and hence is the probability of finding the particle in the eigenstate $n$.