The question asks whether the average of three test scores is equal to the median of the scores. The stem provides that the total of the three scores is 90. From this, the average can be calculated as 90 / 3 = 30. The question can therefore be rephrased as: "Is the median of the three scores equal to 30?".
Statement (1) states that Yuki's score was 20 greater than Stephen's score. Let the scores be J, Y, and S. We have Y = S + 20 and J + Y + S = 90. This simplifies to J + 2S = 70. This single equation does not determine unique values for the scores. For example, if S=20, then Y=40 and J=30; the scores {20, 30, 40} have a median of 30. However, if S=25, then Y=45 and J=20; the scores {20, 25, 45} have a median of 25. Since the median is not always 30, this statement is insufficient.
Statement (2) states that Jacob's score was 30. Since the average of the three scores is 30, this means one of the scores is equal to the average. For any set of three numbers, if one of the numbers is equal to the average of the set, that number must also be the median. To prove this, let the scores be {30, Y, S}. We know 30 + Y + S = 90, so Y + S = 60. If Y=S, they must both be 30, and the median is 30. If Y and S are not equal, one must be greater than 30 and one must be less than 30. When the three scores are ordered, 30 will always be the middle value. Therefore, the median must be 30. This statement provides a definitive "Yes" answer to the rephrased question.
Statement (2) alone is sufficient, but statement (1) alone is not. The correct answer is (B).