What is the 2 sided confidence interval for the mean strength of a new structural column? The sample size is 25, the mean is 15,000 pounds, and the sample standard deviation is 200 lbs. Use a confidence level of 95 %.
What is the 2 sided confidence interval for the mean strength of a new structural column? The sample size is 25, the mean is 15,000 pounds, and the sample standard deviation is 200 lbs. Use a confidence level of 95 %.
This is a simple substitution into a standard formula that should be in your textbook or class notes. The formula is here too: 1.3.5.2. Confidence Limits for the Mean.
Where exactly are you stuck?
The formula in the link I gave you is $\displaystyle \overline{Y} \pm t_{\alpha/2, \, N-1} \frac{s}{\sqrt{N}}$.
Substitute $\displaystyle \overline{Y} = 15,000$, $\displaystyle s = 200$ and $\displaystyle N = 25$.
$\displaystyle \alpha = 0.05$ and $\displaystyle N = 25$ mean that you require the value of $\displaystyle t_{\alpha/2, \, N-1} = t_{0.025, \, 24}$ (24 is the number of degrees of freedom). From a standard table of critical values I get $\displaystyle t_{0.025, \, 24} = 2.064$.
Substitute all this into the formula to get your confidence interval.