Que: 44, 52, 56, 65, 73, 75, 77, 95, 96, 97
The list above shows the scores of 10 students obtained on a scheduled test. If the standard deviation of the 10 scores is 20.50, how many of the scores are greater than one standard deviation above the mean of the 10 scores?
(A) None
(B) One
(C) Two
(D) Three
(E) Four
Solution: Question asks the number of scores > (Mean + S.D.)=> Mean = (44 + 52 + 56 + 65 + 73 + 75 + 77 + 95 + 96 + 97) / 10 = 730 / 10 = 73
=> S.D. = 20.50. Thus,
=> Mean + S.D. = 73 + 20.50 = 93.50
It is clear that three scores (95, 96, and 97) are greater than 93.50.
Therefore, D is the correct answer.
Answer D