More stats than excel

Looking for a way to predict frequency of a range of values based on a mean and standard deviation.

For example:

I know that my mean is 160 and my standard deviation is 20 and I know that ~68% of my values will fall between 140 and 180 but how can I predict how many values will fall between 140 to 150? or 200 to 250, or etc.

Thanks.

If I understand my stats correctly (and I tested this with values of 180 and 140 and got ~68%, you can use =NORMDIST(250,160,20,1)-NORMDIST(200,160,20,1)