You can use a t-test to find the percentage of the bell curve that is below a certain point by converting X to a t-score. Convert from percentage to number of scores by multiplying by N. I'm not 100% sure, but if I encountered such a problem on a test, that's how I would go about doing it.
edit: For reference...
<pre>t = (x - u)/s</pre>where u - mean, s - stdev. Then use a calculator function or something (or do the integral by hand) to get the percent area to the left, then multiply by N. If I understand correctly, you should get nb.
OOC: How do you do superscripts and subscripts?
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