Members of the school committee for a large city claim that the population mean class size of a middle school class within the district is exactly 20 students. Karla, the superintendent of schools for the city, thinks the population mean is less. She selects a random sample of 35 middle school classes across the city. The sample mean is 18.5 students with a sample standard deviation of 3.7 students. The test statistic t for a hypothesis test of H0:μ=20 versus Ha:μ<20 is t≈−2.40. If 0.01

At a level of dignificance of 0.01, there is not enough evidence to support the claim that the population mean class size of a middle school class within the district is less than 20.

P-value = 0.011

Step-by-step explanation:

This is a hypothesis test for the population mean.

The claim is that the population mean class size of a middle school class within the district is less than 20.

Then, the null and alternative hypothesis are:

The significance level is 0.01.

The sample has a size n=35.

The sample mean is M=18.5.

As the standard deviation of the population is not known, we estimate it with the sample standard deviation, that has a value of s=3.7.

The estimated standard error of the mean is computed using the formula:

Then, we can calculate the t-statistic as:

The degrees of freedom for this sample size are:

This test is a left-tailed test, with 34 degrees of freedom and t=-2.398, so the P-value for this test is calculated as (using a t-table):

As the P-value (0.011) is bigger than the significance level (0.01), the effect is not significant.

The null hypothesis failed to be rejected.

There is not enough evidence to support the claim that the population mean class size of a middle school class within the district is less than 20.

correct

step-by-step explanation: