Answer: n=156, x-bar=80, standard deviation σ =24, %=95
Standard error, SE= σ/√n =24/√156
=24/12.49=1.92
For 95% z-score = 1.96
So, the width of the confidence interval=z*SE = 1.96*1.92=3.7632
Lower Limit=x-bar - width= 80-3.7632= 76.2368
Upper Limit=x-bar + width= 80+3.7632= 83.7632
So, the confidence intervals is [76.2368, 83.7632] (Ans.) Edit

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