Answer: The confidence interval is 1.69ppb±0.055
Step-by-step explanation:
To find the confidence interval, first find the z* which is the appropriate z*-value related to the confidence interval of preference. As in this is 95%, z*-value = 1.96 (Note: The value is from the standard normal Z distribution).
With the z*-value, multiply by the division of the standard deviation and the square root of the sample size:
z*-value . σ/√n = 1.96 · [tex]\frac{0.25}{\sqrt{80} }[/tex] = 0.055
The 95% confidence interval of the sample mean of 1.69 ppb is 1.69ppb±0.055ppb
