The 80% confidence interval states that 95% of the sample means of a specified sample size selected from a population will lie within plus and minus 1.28 standard deviations of the hypothesized population mean.
Solution :
At 80% confidence level the z is ,
= 1 - 80% = 1 - 0.80 = 0.20
/ 2 = 0.20 / 2 = 0.10
Z/2 = Z0.10 = 1.28
The 80% confidence interval states that 90% of the sample means of a specified sample size selected from a population will lie within plus and minus 1.28 standard deviations of the hypothesized population mean .
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