Answer: 20
Step-by-step explanation:
Formula to find the sample size : [tex]n=(\dfrac{\sigma\times z_{\alpha/2}}{E})^2[/tex]
Given : Significance level : [tex]\alpha=1-0.95=0.05[/tex]
Critical value : [tex]z_{\alpha/2}=1.96[/tex]
Margin of error : [tex]E<\text{2 hours}[/tex]
Standard deviation: [tex]\sigma=\text{ 4.5 hours}[/tex]
Then, we have
[tex]n=(\dfrac{4.5\times(1.96)}{2})^2=19.4481\approx20[/tex]
Hence, the minimum sample size must be 20.
