Answer:
306
Step-by-step explanation:
The sample size n in Simple Random Sampling is given by
[tex] \bf n=\frac{z^2s^2}{e^2}[/tex]
where
z = 1.2816 is the critical value for a 80% confidence level (*)
s = 1.5 is the estimated population standard deviation
e = 0.11 points is the margin of error
so
[tex]\bf n=\frac{z^2s^2}{e^2}=\frac{(1.2816)^2(1.5)^2}{(0.11)^2}=305.42\approx 306[/tex]
rounded up to the nearest integer.
(*)This is a point z such that the area under the Normal curve N(0,1) inside the interval [-z, z] equals 80% = 0.8
It can be obtained in Excel or OpenOffice Calc with
NORMSINV(0.9)
