Que: 40, 50, 60, 70, 80, 90, 100, 110, 120, 130 The list above shows......

[Max@Math Revolution]

Que: 40, 50, 60, 70, 80, 90, 100, 110, 120, 130

The list above shows the scores of 10 students obtained on a scheduled test. If the standard deviation of the 10 scores is 30.28, 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

[Max@Math Revolution]

Solution: Question asks the number of scores > (Mean + S.D.)

=> Mean = \(\frac{\left(40+50+60+70+80+90+100+110+120+130\right)}{10}=\frac{850}{10}=85\)

=> S.D. = 30.28. Thus,

=> Mean + S.D. = 85 + 30.28 = 115.28

It is clear that three scores (120 and 130) are greater than 115.28.

Therefore, C is the correct answer.

Answer C