$n = \frac{(1.96) (0.25)}{(0.03)^2}$

$n = \frac{(1.96) (0.5)}{(0.03)^2}$

$n = \frac{(1.96)^2 (0.25)}{(0.03)^2}$

$n = \frac{(1.96)^2 (0.5)}{(0.03)}$