Wielkość próby i margines błędu w przedziale ufności dla średniej

Jeremiah wants to estimate the mean age of students at his large university. He'll sample $n$‍ students and make a $95\mathrm{\%}$‍ confidence interval for the mean age. He is willing to use $\sigma =3$‍ years as an estimate of the standard deviation, and he wants the margin of error to be no more than $1$‍ year.