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(20062)  (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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