here is how i approach it:
1) the purpose of standard deviation is to be added to or subtracted ([font=lucida sans unicode]±) from the mean value to give you a range of values
2) so, the mathematical application is:
range = 85 [font=lucida sans unicode]± 25
3) determining the range:
upper limit (addition) = 85 + 25 = 110 mg/dl
lower limit (subtraction) = 85 - 25 = 60 mg/dl
so, the range of her blood glucose level is somewhere between 60 mg/dl and 110 mg/dl.
now, normal distribution means a regular bell-curve, which means this calculation satisfies the range of values as well.
you should be able to calculate the rest by using the eqn
shown above for each section of the bell-curve.
here also is a helpful site: http://stattrek.com/lesson2/normal.aspx