# Confidence interval for the true mean of all scores

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The standard deviation of test scores on a certain achievement test is 10.8 . A random sample of 80 scores on this test had a mean of 75.4 . Based on this sample, find a 90% confidence interval for the true mean of all scores. Then complete the table below.

Carry your intermediate computations to at least three decimal places. Round your answers to one decimal place.

1. What is the lower limit of the 90% confidence interval? __________

2. What is the upper limit of the 90% confidence interval? __________

See attached file for full problem description.

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#### Solution Summary

Calculates the confidence interval for the true mean of all scores.

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