# Standard Deviation

An irate student complained the the cost of textbooks was too high. He randomly surveyed 26 other students and found that the mean amount of money spent for textbooks was $121.60. If the standard deviation of the population was $6.36, find the best point estimate and the 90% confidence interval of the true mean.

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#### Solution Preview

To find the 90% confidence interval, we are look for 2 values a and b such that:

P(X < a) = 5% and P(X > b) = 5% (i.e. P(X <=b ...

#### Solution Summary

This solution calculates the true mean for a given problem.

$2.19