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Help with math questions?
1) The scores on a test resulted in a normal distribution with a mean of 72 and a standard deviation of 9. Approximately what percent scores above 90?
1)2.5%
2)5%
3)10%
4)15%
2) Which of these might change the shape of a distribution?
1) Mean
2)Mode
3)Degrees of freedom
4)Median
2 Answers
- ?Lv 67 years ago
So 90 is 2 standard deviations above 72, The closest one is 2.5%
Changing the mode would definitely change the shape, as in a normal distribution, most of the scores occur near the mean, and taper off away from the mean. If the mode was higher or lower than the mean, then it is no longer a normal distribution, so it has a different shape.
Source(s): http://davidmlane.com/hyperstat/z_table.html - ?Lv 77 years ago
1) z = (X-Mean)/SD
z = (90-72)/9 = + 2
Required percent = P(X > 90) * 100
= P(z > 2) * 100
= 0.0228*100
= 2.28% according to the z-scores chart
2.5% is according to the Empirical Rule 68-95-99.7
CHOICE (1) is the answer
2) Degrees of freedom