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In a random sample of 80 students in first grade, the mean hours of sleep per night was 9.4 with a standard deviation of 0.41. In a random sample of 50 students in 12th grade, the mean hours of sleep per night was 7.5 with a standard deviation of 0.52.

Which interval is a 99% confidence interval for the difference between the mean hours of sleep?


(1.75 h, 2.05 h)


(1.89 h, 1.91 h)


(1.43 h, 2.37 h)


(1.68 h, 2.12 h)

 
 Mar 9, 2020

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