The mistake he made is that he Yuri divided by n instead of n -1.
<h3>What mistake did he make?
</h3>
Standard deviation is used to determine how the values in a group differs from the mean of the values in the group.
In order to determine the standard deviation, take the following steps:
• Determine the mean of the observation: 14
Determine the difference between each value and the mean and then square the result: (12 - 14)² + (14 - 14)² + (9 - 14)² + (21 - 14)² = 78
Determine the mean of the sum of the squared differences and then find the square root of the mean: √78/(n - 1) = 5.1
To learn more about standard deviation, please check: brainly.com/question/26201837
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