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hmdp4
 3 years ago
Standard normal distribution question!!
assume that adults have IQ scores that are normally distributed with a mean of 100 and a standard deviation 20. Find P15, which is the IQ score separating the bottom 15% from the top 85%.
how do i find this!
hmdp4
 3 years ago
Standard normal distribution question!! assume that adults have IQ scores that are normally distributed with a mean of 100 and a standard deviation 20. Find P15, which is the IQ score separating the bottom 15% from the top 85%. how do i find this!

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CliffSedge
 3 years ago
Best ResponseYou've already chosen the best response.0You're looking for the 15th percentile. You need to find the zscore corresponding to a proportion/probability of 0.1500, then use the zscore formula to solve for x.

CliffSedge
 3 years ago
Best ResponseYou've already chosen the best response.0This site is rather good for straightforward notes and formulas: http://stattrek.com/probabilitydistributions/standardnormal.aspx?Tutorial=Stat

CliffSedge
 3 years ago
Best ResponseYou've already chosen the best response.0dw:1349413921591:dw

CliffSedge
 3 years ago
Best ResponseYou've already chosen the best response.0Here's a Ztable if you need it: http://www.math.unb.ca/~knight/utility/NormTble.htm

CliffSedge
 3 years ago
Best ResponseYou've already chosen the best response.0Do you have a calculator with an inverse normal function?

CliffSedge
 3 years ago
Best ResponseYou've already chosen the best response.0If not, you'll need to use that ztable that I linked to. Find the P=0.1500 in the body of the table and read across to the margins to find the associated Zscore. Sometimes you have to estimate between two values and pick the closest one. follow the stattrek.com link to get the zscore formula, plug in your z, µ, and σ, and solve for x.
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