Jacob, Yuki, and Stephen
Total of their scores on the test was 90
Was the average (arithmetic mean) of the 3 scores equal to the median of the 3 scores?
We know that, average of the 3 scores = 90/3 = 30
Need to check if the median is same as mean
Given statements,
(1) Yuki's score was 20 greater than Stephen’s score.
Let Stepehen score = x
=> Yuki = x + 20
Jacob = y
=> Total = x+x+20+y = 90
=> 2x + y = 70
=> y = 70-2x
This is solved for multiple values,
x = 20 => y = 70-40 = 30 => Scores are 20,30,40
=> Median = 30 , Average = 30
Median = Average
x = 15 => y = 70-30 = 40 => Scores are 15,35,40
=> Median = 35, Average = 30
Median!=Average
Statement (1) is NOT sufficient
(2) Jacob's score was 30.
Let Stephen and Yuki score be x and y
=> x+30+y=90
=> x + y =60
From this we can say that,
Among x and y, one has to be greater than 30 and one lesser than 30 to satisfy the above condition
Due to this condition 30 is the middle number making it the median number
=> Average = Median for all possibilities
So,
B. Statement (2) ALONE is sufficient, but statement (1) alone is not.