SOLUTION: What percentage of scores fall between -1 and +1 standard deviation units on a normal curve? How do you know this?

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Question 1141745: What percentage of scores fall between -1 and +1 standard deviation units on a normal curve? How do you know this?
Found 2 solutions by VFBundy, Edwin McCravy:
Answer by VFBundy(438)   (Show Source): You can put this solution on YOUR website!
A z-score that is 1 standard deviation above the mean is +1.0. When you look up +1.0 on a z-table, you get 0.8413. These are the percentage of scores under the curve that are less than +1 standard deviations.

A z-score that is 1 standard deviation below the mean is -1.0. When you look up -1.0 on a z-table, you get 0.1587. These are the percentage of scores under the curve that are less than -1 standard deviations.

To find where these scores intersect...that is, the percentage of scores between -1 and +1 standard deviations...you simply subtract the difference. So, 0.8413 minus 0.1587 is 0.6826.

So, 0.6813 of the scores fall between -1 and +1 standard deviations.
Answer by Edwin McCravy(20063)   (Show Source): You can put this solution on YOUR website!
On your TI 83 or 84, 

press 2ND 
press VARS 
highlight 2:normalcdf
press ENTER        

if you have a newer model 84 calculator, make it read this way

         lower:-1 
         upper: 1 
         m:0 
                  s:1
         Paste 

Press ENTER

You'll read

normalcdf(-1,1,0,1)  

press ENTER, read 0.6826894809

If you have an older model 84 or an 83, make it read 

normalcdf(-1,1,0,1) 

press ENTER, read 0.6826894809

Edwin
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