SOLUTION: a mean score on a standardized test is 50 with a standard deviation of 10. (a)What scores fall between -1 and +1 standard deviation? (b) What percent of all scores fall between -1

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Question 610145: a mean score on a standardized test is 50 with a standard deviation of 10. (a)What scores fall between -1 and +1 standard deviation? (b) What percent of all scores fall between -1 and +1 standard deviation? (c) What score falls at +2 standard deviations? (d)What percentage of scores falls between +1 and +2 standard deviation?
I have: a. 50+10=60, 50-10=40
b. 60%,40%
c. n/a
d. 40%, 30%
What did I do wrong?
Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!
 

Hi,

 a mean score on a standardized test is 50 with a standard deviation of 10.

(a)What scores 'x' fall between -1 and +1 standard deviation? 40 < x <60

(b) What percent of all scores fall between -1 and +1 standard deviation? ~68%

(c) What scores falls at +2 standard deviations? 70

(d)What percentage of scores falls between +1 and +2 standard deviation? 95.4-68.2 = 27.2%

For the normal distribution: 

one  standard deviation from the mean accounts for about 68.2% of the set 

two standard deviations from the mean account for about 95.4%

and three standard deviations from the mean account for about 99.7%.