Final answer:
The deviation score for x = 28 in a population with a mean (μ) of 20 is +8, corresponding to option (a).
Step-by-step explanation:
In a population with μ = 20, the deviation score for x = 28 is calculated by finding the difference between the individual score and the mean. The formula for a deviation score is x - μ, so we substitute our values to get 28 - 20 which equals +8. Therefore, the deviation score for x = 28 is +8, which corresponds to option (a).