Graphs and standard deviation & CiCi's

Preparing for the test
Your test is Thursday. Begin to prepare now by working problems and creating an outline.

Homework: For those in class today - rewrite your responses to the FR questions, plus work problem 1.4 from the text.

For those absent today: Problem 1.4 PLUS ALL OF 1.48-1.52. Pick up your original responses to the FR upon your return to complete overnight. If you were participating in Senior Skip Day, your absence is unexcused.

CiCI's
YES!!!! There is a request for CiCi's this Sunday, so I will be there from 2 to 4. That is the one by the Walmart at Trickum and 92 (close to Arby's).

Test is Thursday, 9/6!

If you are going on the marketing fieldtrip, stay after school to take the test in room 214 at 3:30. Don't forget to bring your calculator.

For Tuesday (9/4), select one odd and one even problem from the set 1.48-1.52 and work them completely. Become an expert on one of the problems.

For Friday (8/31), complete problems 1.41 and 1.43. The answers are in the back of the book, but that is not sufficient! You must show all work and explain your actions.



By Thursday (8/30), you should have both the graph from the Internet, a newspaper, or magazine and problems 1.35 and 1.36 from the text.

RE: the graph
You will identify the variable(s) represented in the graph and the type of graph you brought. Are the data numerical or categorical? Are numerical data discrete or continuous? Does your graph represent one variables or two? Is a trendline appropriate for your data?

RE: Standard deviation

The standard deviation of a sample of data is like an average deviation from the sample mean. It is the square root of the sample variance, which is an unbiased estimator of the population variance.

If we just found the sum of the deviations, we would get a sum of zero because some data are above the mean and some are below. Because of the definition of the mean, the positives and the negatives cancel each other out.

Instead, we square each deviation so the numbers we add together are all positive. We "average" these numbers by dividing by (n-1). You remember that n is the number of observations. We subtract one because we are using an estimate derived from the data themselves for x-bar. This gives us the sample variance or s-squared. To get the value of s just take the square root.

In formula form, s = sqrt(sum of all the squared deviations/(n-1)). The formula for the first squared deviation is (x minus x-bar)^2. Again, x-bar is the average of the x values.

The same relationship holds between sigma and sigma squared, the population standard deviation and the population variance: you take the square root of the variance to get the standard deviation.