Final answer:
A related-samples t-test should be used to determine if answering questions while studying produced significantly higher scores.
Step-by-step explanation:
To determine if answering questions while studying produced significantly higher scores, a related-samples t-test should be used. This is because the same group of students was tested under two different conditions - answering questions and simply rereading the material. The mean and standard deviation of the group who answered questions were 78.3 and 8.4, respectively. By conducting a related-samples t-test and comparing the means of the two conditions, we can determine if the difference in scores is statistically significant.