In the previous section we discovered how to make a confidence interval for estimating population mean. However we knew what the population standard deviation (σ) was. However it is not always the case that σ is known.
If population standard deviation (σ) is unknown then to make a confidence interval to estimate population mean we cannot our old formula for error: E=Z2σ∗√nσ as it requires a knowledge of σ. So instead we are required to use a thing called t-scores (t2α).
Once we find the t-scores for particular values (this is done in a similar way to finding z-scores) we have a new formula for the Margin of Error: E=Z2σ∗√nS
In “Anchiles”, a small made-up town near the equator, 15 random days were sampled and found to have an average temperature of 28°C, with a standard deviation of 4°C. Assume that the average daily temperature of this town is normally distributed.
Don't just watch, practice makes perfect.
We have over 310 practice questions in Statistics for you to master.