Asample data set has a mean of 122.3 and a standard deviation of 18.5. convert a score of 168.4 to a z score and determine if the score is "usual" or "unusual" 1.23; usual -1.23; usual d.49; unusual -2.49; unusual

Given mean =122.3 and standard deviation =18.5

                                                                   ≈2.49

As a general rule z-scores lower than -1.96 or higher than 1.96 are considered unusual.

Since our z-score = 2.49>1.96 , it is unusual.

Hence correct option is 'C'  = "2.49 ; unusual"