Question

Yuri computes the mean and standard deviation for the sample data set 12, 14, 9, and 21. He finds the mean is 14. His steps for finding the standard deviation are below.

s = StartRoot StartFraction (12 minus 14) squared + (14 minus 14) squared + (9 minus 14) squared + (21 minus 14) squared Over 4 EndFraction EndRoot. = StartRoot StartFraction negative 2 squared + 0 squared + negative 5 squared + 7 squared Over 4 EndFraction EndRoot. = StartRoot StartFraction 4 + 0 + 25 + 49 Over 4 EndFraction EndRoot. = StartRoot StartFraction 78 Over 4 EndFraction EndRoot. = StartRoot 19.5 EndRoot.

What is the first error he made in computing the standard deviation?
A. Yuri failed to find the difference between each data point and the mean.
B. Yuri divided by n instead of n -1.
C. Yuri did not subtract 9 - 14 correctly.
D. Yuri failed to square -2 correctly.

Answer 1

B.

Explanation:

(Here's Answers for the Quiz I did so far!)

1. Abby is collecting rainfall data.

Answer: B.

2. The Monthly Mean Salaries

Answer: A.

3. The Number of Cars at a Dealer Ship

Answer: A. (6.9)

4. The Mean Set of Credit Card Scores.

Answer: C. (720)

Answer 2

B. Yuri divided by n instead of n-1

Explanation:

It was stated in the question that the dataset was sample dataset. For a sample dataset, the standard deviation is given by the formula,

σ = √ Σ (Xi - mean)²/(n - 1) where i = 1,2,3.....n

Since this is just a sample dataset and not the whole population, Yuri should have divided by n-1 instead of n.