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Confidence Intervals and corresponding z-scores

A cutoff score of 79 has been established for a sample of scores in which the mean is 65. If the corresponding z-score is 1.4 and the scores are normally distributed, what is the standard deviation?

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Solution. Assume that the standard deviation is x, by the hypothesis, we know that

|79-65|/x=1.4, so x=10

that is,
the ...

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