OG详解-OG2 数学1 Q9

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 5+9+9+134​​or 9, and the mean of data set Y is 5+9+9+13+275​​, 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.
Choice A is incorrect and may result from conceptual or calculation errors. 
Choice C is incorrect and may result from conceptual or calculation errors. 
Choice D is incorrect and may result from conceptual or calculation errors.