A sample of a non-stoichiometric iron oxide compound has the empirical formula \(\text{Fe}_{0.80}\text{O}\). The solid consists of a crystal lattice containing only \(\text{Fe}^{2+}\), \(\text{Fe}^{3+}\), and \(\text{O}^{2-}\) ions. Assuming the crystal lattice is electrically neutral, what fraction of the total iron cations in the sample are \(\text{Fe}^{3+}\)?