Question 40844
There are different margin of error formulas relating 
to different population parameters.
If you are talking about the margin associated with 
estimating the mean of a population 
the margin of error is E=z(star)[s/sqrt(n)]

Solve this equation for n as follows:

sqrt(n)= z(star)[s/E]

Square both sides to get:
 
n=[z(star)s/E]^2

Cheers,
Stan H.