Miss Romero noted that the mean scores of a random sample of 15 grade 8 students who had taken a special test were 80.5. If the standard deviation of the scores was 3.1 and the sample came from an approximety normal population, find the interval estimate of the population mean, using 95% confidence
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3$\begingroup$ Richard, this is a homework question, so you need to add the tag "self-study" to it. You need to explain what you tried in order to solve the question and where you got stuck so that people can help you. For example, is it that you are not sure what formula to use to compute a confidence interval for a population mean? Or that you don't understand the concept of a confidence interval? Since it os your homework, you have to give yourself the best chance of solving it by asking for targeted help. $\endgroup$– Isabella GhementCommented Feb 21, 2019 at 14:55
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1$\begingroup$ Oh okay ma'am, i edited it now. I needed the answer asap bc idk about that topic, that's just a example from my book. $\endgroup$– Richard GalamitonCommented Feb 21, 2019 at 14:57
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1 Answer
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Assuming a normal distribution:
Subtract 1.95*3.1/sqrt(8) to the mean. That's the lower bound.
Add 1.95*3.1/sqrt(8) times the standard deviation to the mean.That's the upper bound.
Sometimes that 1.95 coefficient will get rounded up to 2. Also, some people define the standard deviation in terms of n (sample size) while others in terms on (n-1). You may have to divide by sqrt(7) instead of sqrt(8)
