SAT Question 55cfaf22: Distributions, Center & Spread answer and explanation with Desmos solution

Choice B is correct. ​​The mean of a data set is the sum of the values in the data set divided by the number of values in the data set. It follows that the mean of data set X is $\frac{5+9+9+13}{4}$, or $9$, and the mean of data set Y is $\frac{5+9+9+13+27}{5}$, or $12.6$. Since $9$ is less than $12.6$, the mean of data set X is less than the mean of data set Y.

Alternate approach: Data set Y consists of the $4$ values in data set X and one additional value, $27$. Since the additional value, $27$, is larger than any value in data set X, the mean of data set X is less than the mean of data set Y.