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MA121: chapter 4 assessment test


Six different brands of Italian salad dressing were randomly selected at a supermarket. The grams of fat per serving are 7, 7, 9, 6, 8, 5. Assume that the underlying distribution is normal. Calculate a 95% confidence interval for the population mean grams of fat per serving of Italian salad dressing sold in supermarkets.

the above problem yields a result of (5.52, 8.48) assuming a t distribution.

Can you please explain why t distribution is considered if the question confirms that the population distribution is normal?


bump…i am also curious why – cannot understand and seems like i cannot get the answer from or so hope some here can provide and explanation…thanks


I think due to very small sample size, even though the population is normally distributed, they had considered t distribution rather than normal distribution.