Question 1141745
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.
<pr>
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.
<pr>
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. 
<pr>
So, 0.6813 of the scores fall between -1 and +1 standard deviations.