First, we know the average is 90 ÷ 3 = 30.
Statement (1): Yuki's score was 20 greater than Stephen's score.
This gives us Y = S + 20, but we don't know what J is. Without knowing all three scores, we can't determine if the median equals 30. Statement (i) alone is insufficient.
Statement (2): Jacob's score was 30.
We know J = 30, but we don't know Y and S individually. Without knowing all three scores, we can't determine if the median equals 30. Statement (2) alone is insufficient.
Statements (1) and (2) combined:
From statement (1): Y = S + 20A
From statement (2): J = 30
We know J+ Y +S = 90, so 30 + (S+ 20) + S= 90
30 + 25 + 20 = 90
2S = 40
S= 20
Therefore, Y = S + 20 = 20 + 20 = 40
The three scores are 20, 30, and 40.
The median is 30, which equals the average.
Therefore, the correct answer is C) Both statements together are sufficient, but neither alone is sufficient.