Question

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

Explanation:

Step1: Recall standard - deviation formula

For a sample, the formula for the standard deviation is $s=\sqrt{\frac{\sum_{i = 1}^{n}(x_{i}-\bar{x})^{2}}{n - 1}}$, where $n$ is the number of data - points, $x_{i}$ are the individual data - points, and $\bar{x}$ is the mean.

Step2: Analyze the given calculation

In the given calculation, the denominator is $n = 4$ instead of $n-1=3$. When calculating the sample standard deviation, we divide by $n - 1$ to get an unbiased estimator.

Answer:

Yun divided by $n$ instead of $n - 1$