91Ó°ÊÓ

In words, define the random variable $X$.

In words, define the random variable $\stackrel{¯}{X}$ .

Construct a $90\%$ confidence interval for the population mean weight of the heads of lettuce. State the confidence interval, sketch the graph and calculate the error bound.

Construct a $95\%$ confidence interval for the population mean weight of the heads of lettuce. State the confidence interval, sketch the graph and calculate the error bound.

In complete sentences, explain why the confidence interval in Exercise 8.17 is larger than in Exercise 8.18.

A sample of $20$heads of lettuce was selected. Assume that the population distribution of head weight is normal. The weight of each head of lettuce was then recorded. The mean weight was $2.2$pounds with a standard deviation of $0.1$pounds. The population standard deviation is known to be $0.2$pounds.

What would happen if $40$ heads of lettuce were sampled instead of $20$, and the confidence level remained the same?

The mean age for all Foothill College students for a recent Fall term was $33.2$. The population standard deviation has been pretty consistent at $15$. Suppose that twenty-five Winter students were randomly selected. The mean age for the sample was $30.4$. We are interested in the true mean age for Winter Foothill College students. Let $X=$the age of a Winter Foothill College student.

$\_\_\_=15$.

The mean age for all Foothill College students for a recent Fall term was $33.2$. The population standard deviation has been pretty consistent at $15$. Suppose that twenty-five Winter students were randomly selected. The mean age for the sample was $30.4$. We are interested in the true mean age for Winter Foothill College students. Let $X=$the age of a Winter Foothill College student.

In words, define the random variable $\stackrel{¯}{X}$.

Which distribution should you use for this problem?

The mean age for all Foothill College students for a recent Fall term was $33.2$. The population standard deviation has been pretty consistent at $15$. Suppose that twenty-five Winter students were randomly selected. The mean age for the sample was $30.4$. We are interested in the true mean age for Winter Foothill College students. Let$X=$ the age of a Winter Foothill College student.

Construct a $95\%$Confidence Interval for the true mean age of Winter Foothill College students.

How much area is in both tails (combined)? $\mathrm{Î\pm }=\_\_\_\_\_$?