If two sets of test scores indicate that Score-Set X has a standard-deviation of 10.2, while Score-Set Y, on the same test, has a standard deviation of 8.4, what does this signify?

The Standard deviation signify how far the values are spread above and below the mean. The score set X has a high standard deviation which shows that the data from the score set X is widely spread and the Score set Y has a low standard deviation which shows that the data are clustered closely around the mean.

Step-by-step explanation:

Comparing the standard deviations of the two score sets and making a conclusion.