Answer:
n = 400
Step-by-step explanation:
The formula for the error in our estimate is given by:
Standard Error : √ ( p(1-p)/ n)
Error = SE = Zα/2 √ ( p(1-p)/ n) where
Zα/2= critical value for 95% confidence level = 1.96
and we know our error is 3.5 %
But we do not the sample proportion p. Then what we can do is give an estimate of p in the absence of any other information.
In this case we will use p= 0.5 which is the value that maximizes the expression for the standard error :
if p = 0.8 then SE= 0.040
p = 0.3 then SE =0.036
p = 0.1 then SE = 0.030
p = 0.5 then SE = 0.050
Substituting
3.5/100 = 1.96 x √ (( 0.5 x 0.5 ) /n )
3.5/ (100 x 1.96 x 0.5 ) = 1/ √n
0.0357 = 1 /√n
n = 20²
n = 400
