## Essentials of Statistics (5th Edition)

$\alpha=1-0.99=0.01.$ Using the table: $z_{\alpha/2}=z_{0.005}=2.575.$ Hence the minimum sample size:$\frac{z_{\alpha/2}^2\cdot 0.25}{E^2}=\frac{2.575^2\cdot 0.25}{0.02^2}\approx4144$.