For testing $H_{0}: \quad \mu=10$ and $H_{1}: \mu \neq 10$, the level of significance, $\alpha=0.05$ is being considered. What sample size is necessary in order for the probability to be 0.1 of falsely failing to reject $H_{0}$ when the true population mean differs from 10 by $0.5 ?$ From a preliminary sample, we estimate the value of $\sigma$ to be $1.25 .$