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. what is the first error he made in computing the standard deviation

Answer 1

the complete question in the attached figure N 1

we know that
The formula for Sample Standard Deviation is indicated in the attached figure N2
n in this problem is 4 and Yuri had to divide in the formula by 3  

therefore

the answer is
 Yuri divided by n instead of n -1