statistics
posted by mike .
a quiz consists of 30 true or false questions. if the student guesses on each question, what is the standard deviation of the number of correct answers

statistics 
PsyDAG
The Range Rule
The range rule tells us that the standard deviation of a sample is approximately equal to one fourth of the range of the data. In other words s = (Maximum – Minimum)/4. This is a very straightforward formula to use, and should only be used as a very rough estimate of the standard deviation.
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