statistics help anybody

so my girlfriend is taking statistics and she just bombed a test, her teacher just gave her the chance to retake a question that will get her to pass if she gets it right, i am not in the class and am pretty much useless...if anybody can help I would really appreciate it...thanks!!!

I am just completely failed my online test and my teacher is letting me retake this 20 point question to try and pass...if anybody can help me out I would really appreciate it.

For a distribution of scores which = 82 and a standard deviation =2.5 I need to find the following:

A: what percentage of scores falls between the mean and a raw score of 84?

B: what is the prob of a score falling above a raw score of 86

C: what is the prob of a score falling between the raw of 83 and 87

D: percentile rank of a score of 79

E: percentile rank of a score of 89

I recieved 2 points on the 20 point question...I am pretty sure I got in over my head with my current class load...any help and pointing me in the right direction would be greatly appreciated.

Thanks
James

 

bump...hoping for statistics buff or somebody in college to read this!

 

its not my class, its my girlfriends

 

Assuming normal distribution and that 82 is the mean.

For A. A graphing calculator helps a lot, but basically if you can find what % falls below 84 then just subtract .5 or 50% because 82 splits the data... data below raw score 84 is .7881- .5 is .2881 or 28.81 percent

To do it without a graphing calculator, take the value (84) subtract the mean (82) and divide by sigma (2.5). Gives you z = .8 Then take a z-table, like this one (http://statstutorstl.blogspot.com/2010/07/z-table-gives-probabilty-distribution.html) and find the corresponding probability value (.7881)

For B. Its the same principal, just find what % is above 86, in this case .0548 or 5.48 percent. Where they're asking the probability i would presume percentage is acceptable but maybe I will stand corrected

C. Same method as A, below 83 is .6554, 65.54 percent of data, below 87 is .9772, .9772 - .6554 = answer. (too lazy)


For D and E, Somone else might chime in, I think you need to know how many people sampled lower than the value and how many total samples there are...

EDIT** from what I am reading about it, sort of seems that the percentile score just becomes that probability value ( for example Percentile score of 87 is 97.72 percentile. I know this isnt giving you the answer but maybe it will turn some wheels and she may be able to recall something from her notes )


Here is a calculator i quickly found for the distribution chart though, TI 83 or equivalent graphing calculators can do the same thing, as well Normal distribution tables can be used. http://easycalculation.com/statistics/normal-distribution.php



You might want to double check all those calculations now that you can see how to do it. I did it rather quickly.


Hopefully I helped a little! Cheers.