A machine produces bolts whose diameters are normally distributed with mean and standard deviation . What percentage of bolts fall between and ?
Answer and explanation
Correct answer: A.
- Step 1: The range corresponds to since . Under the empirical rule for a normal distribution, approximately of observations lie within two standard deviations of the mean. **Answer: . Why not the others:** corresponds to one standard deviation, corresponds to three standard deviations, and is not a standard empirical landmark.
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