Answer: The required sample size = 97
Step-by-step explanation:
If prior population standard deviation is known, then the minimum sample size can be computed as:
[tex]n=(\frac{z^*\times\sigma}{E})^2[/tex]
,where z* = critical z-value
[tex]\sigma[/tex] = population standard deviation
E = Margin of error
As per given,
[tex]\sigma=20,\ E= 4[/tex]
Critical value for 95% confidence = 1.96
[tex]n=(\frac{1.96\times20}{4})^2\\= (1.96\times 5)^2\\= (9.8)^2\\=96.04\approx97[/tex]
Hence, the required sample size = 97
