In a certain normal distribution of scores, the mean is 30 and the standard deviation is 3. Find the z-score corresponding to a score of 23.

Use the z-score formula: z = (score − mean) ÷ standard deviation. Substituting the values gives (23 − 30) ÷ 3 = −7 ÷ 3 ≈ −2.33, so the z-score is choice D, −2.33.

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