a) The confidence interval is exact for normal populations and is approximately correct for large samples from non-normal populations. 1. For small samples, say, of size less than 15, the z-interval procedure should be used only when the variable under consideration is normally distributed or very close to being so.
b)The provided sample mean is X = 218 and the population standard deviation is σ=72. The size of the sample is n = 26 and the required confidence level is 10%.
Based on the provided information,Using z table the critical z-value for α=0.1 is zc=1.645.
Formula to find confidence interval:
which completes the calculation.
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