Answer: 95% confidence interval is (29.38, 30.62).
Step-by-step explanation:
Since we have given that
n = Sample size = 40
Average value = 30 miles per hour
Standard deviation = 2 miles per hour
We need to find the interval for 95% confidence interval.
So, z = 1.96
So, the intervals would be
[tex]\bar{x}\pm z\dfrac{\sigma}{\sqrt{n}}\\\\=30\pm 1.96\times \dfrac{2}{\sqrt{40}}\\\\=30\pm 0.62\\\\=(30-0.62,30+0.62)\\\\=(29.38,30.62)[/tex]
Hence, 95% confidence interval is (29.38, 30.62).