2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/208952What are the prices of random variables? In this paper, we define the least-squares prices of coin-flipping games, which are proved to be minimal, positive linear, and arbitrage-free. These prices depend both on a set of games that are available for investing simultaneously and on a risk-free interest rate. In addition, we show a case where the mean-variance portfolio theory is inappropriate.6 pages. We added Remarks 3.5 and 3.6. We revised Remark 3.6Optimization and ControlStatistical Finance91B24 (Primary); 91B28 (Secondary)text