In: Statistics and Probability
Let X equal the excess weight of soap in a "1000-gram" bottle.
Assume that the distribution of XN(μ,180).
What sample size is required so that we have 95% confidence that
the maximum error of the estimate of μ is 1.7?
Sample size required= ?
given , σ² =180
σ=√σ² = √180 = 13.4164
sampling error ,    E =   1.7  
           
   
Confidence Level ,   CL=   95%  
           
   
          
           
   
alpha =   1-CL =   5%  
           
   
Z value =    Zα/2 =    1.960   [excel
formula =normsinv(α/2)]      
       
          
           
   
Sample Size,n = (Z * σ / E )² = (   1.960  
*   13.4164 /   1.7   ) ²
=   239.3
          
           
   
          
           
   
So,Sample Size
needed=       240