2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/89173The first two period behaviors of a quantum wave packet in an infinite square well potential is studied. First, the short term behavior of expectation value of a quantity on an equally weighted wave packet (EWWP) is in classical limit proved to reproduce the Fej'{e}r average of the Fourier series decomposition of the corresponding classical quantity. Second, in order to best mimic the classical behavior, a nice relation between number $N$ of stationary states in the EWWP with the average quantum number $n$ as $N\thickapprox \sqrt{n}$ is revealed. Third, since the Fejér average can only approximate the classical quantity, it carries an uncertainty which in large quantum number case is almost the same as the quantum uncertainty.Revtex, 4 pages, 4 figuresQuantum Physicstext