The cycle times for an electroplating machine are believed to be normally distributed. Twenty-one plating operations are randomly sampled, and cycle times are recorded. The sample average cycle time is 10.21 min, with a standard deviation of 0.59 min. What is a 95% confidence interval for the mean cycle time on this machine?
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(9.958, 10.462)
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(9.941, 10.479)
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(8.979, 11.441)
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(9.911, 10.509)