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Answer: the required sample size = 155
Step-by-step explanation:
If the standard deviation of the prior study is known, then the formula to compute required sample size:
[tex]n=(\frac{z^*\times\sigma}{E})^2[/tex], where E = Margin of error, z* = Critical value, [tex]\sigma[/tex] = populion standard deviation.
Given: E = 3.7 , [tex]\sigma=28[/tex]
Critical value for 90% confidence = 1.645
Required sample size: [tex]n=(\frac{1.645\times28}{3.7})^2[/tex]
[tex]n=(12.4486486486)^2\approx155[/tex]
Hence, the required sample size = 155