Answer:
Given,
n = 1600
E = +/- 0.0343%
Here for 95% confidence interval , z value is 1.96
Now consider,
n = (z*s/E)^2
from this,
E = z*s/sqrt(n)
substitute values
0.000343 = 1.96*s/sqrt(1600)
0.000343 = 1.96*s/40
s = 0.000343*40 / 1.96
s = 0.007
Now to give the sample size for 85% confidence interval & E = 0.05
consider,
n = (z*s/E)^2
Here for 85% confidence interval , z value is 1.44
n = (1.44*0.007 / 0.05)^2
= 0.04064
= 4*10^-2
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