mathematics, education, statistics

A worksheet on the Internet purported to be about standard deviation. In theory, students needed to do a lot of arithmetic to arrive at the figure. However some proved adept at finding the *key* online and copying down the language describing what "standard deviation" means. This caught my eye, but in the moment I was almost as disturbed by the key's language:

Quote:

(Data set): 2,3,5,7,8,10,11,11,13,15,17,18 [It asks students to find the mean, then gives calculator instructions for finding the mean and standard deviation] Q. What does the standard deviation mean in this case? A. The numbers in the list are an average of 5.21 units away from 9.9.

Three issues:

1: The mean of that data set isn't 9.9, it's 10.
2. Second, per the standard deviation calculator on mathisfun, the standard deviation is 5, not 5.21.
3. Students are asked "what it means" and the key says "the average distance of all of the numbers in a list from the mean."

No, that's the *mean absolute deviation*. Standard deviation is the square root of the average squared distances from the mean.

What am I getting wrong here? This came from a college website. I encourage high school students to use online resources but it never occurred to me they would simply search for the key. I'd like to check all the answers, but I don't have time right now.

via International Skeptics Forum http://ift.tt/2gK3Dsd