U.S. companies lose $63.2 billion per year from workers with insomnia. Accordign to a 2013 article in the Wall Street Journal, workers lose an average of 7.8 days of productivity per year due to lack of sleep. The following data show the number of hours of sleep attained during a recent night for a sample of 20 workers.

a. What is the mean number of hours of sleep for this sample?

b. What is the variance? Standard deviation?

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