## Elementary Statistics (12th Edition)

$\alpha=1-0.98=0.02.$ Using the table: $z_{\alpha/2}=z_{0.01}=2.33.$ Standard deviation=$\frac{range}{4}=\frac{2400-600}{4}=450.$ Hence the sample size:$\left (\frac{z_{\alpha/2}\cdot \sigma}{E}\right)^2=\left (\frac{2.33\cdot450}{100}\right)^2\approx110$.It isn't right that the standard deviation is estimated, because we have to know the exact value.