Answer:
The minimum sample size required is 25 so that margin of error is no more than 3 minutes. Â
Step-by-step explanation:
We are given the following in the question:
Mean, μ = 42 minutes
Standard Deviation, σ = 9 minutes.
We want to build a 90% confidence interval such that margin of error is no more than 3 minutes.
Formula for margin of error:
[tex]z_{critical}\times \dfrac{\sigma}{\sqrt{n}}[/tex]
[tex]z_{critical}\text{ at}~\alpha_{0.10} = 1.64[/tex]
Putting values, we get.
[tex]z_{critical}\times \dfrac{\sigma}{\sqrt{n}}\leq 3\\\\1.64\times \dfrac{9}{\sqrt{n}}\leq 3\\\\\dfrac{1.64\times 9}{3}\leq \sqrt{n}\\\\4.92\leq \sqrt{n}\\\Rightarrow n\geq 24.2064\approx 25[/tex]
Thus, the minimum sample size required is 25 so that margin of error is no more than 3 minutes.
