## Question 682:

1## Answer:

No answer provided yet.When testing a single mean you test against a criteria or benchmark (say is the mean greater than 0). When comparing two means you are comparing the means and standard deviations from two different samples.

When using the z-test the two assumptions are you need to know the population standard deviation and the data are normally distributed with a reasonably large sample size (usually n >30).

The sample standard deviations can typically be used in place of the population standard deviations when the sample size is large (n >30).