The scores of a test given to students are normally distributed with a mean of 21. If 80% of the students have scores less than 23.7, what is the standard deviation of the scores?

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The scores of a test given to students is normally distributed. The mean is 21. 80% of students have a score less than 23.7. Let the standard deviation be S.

The z-score that corresponds to a probablity of 80% is 0.84

`(23.7 - 21)/S` = 0.84

=> S = 3.214

The standard deviation is 3.214

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