According to the Sleep Foundation, the average night's sleep is 6.8 hours (Fortune, March 20, 2006). Assume the standard deviation is .5 hours and that the probability distribution is normal.

1. What is the probability that a randomly selected person sleeps more than 8 hours (to 4 decimals)?
4. What is the probability that a randomly selected person sleeps 6 hours or less (to 4 decimals)?
7. Doctors suggest getting between 7 and 9 hours of sleep each night. Whatpercentageof the population gets this much sleep (to the nearest whole number)?

The time needed to complete a final examination in a particular college course is normally distributed with a mean of 77 minutes and a standard deviation of 12 minutes.? Answer the following questions.

1. What is the probability of completing the exam in one hour or less (to 4 decimals)?

eBookVideo{Exercise 6.18}

The average return for large-cap domestic stock funds over the three years 2009-2011 was 14.7%. Assume the three-year returns were normally distributed across funds with a standard deviation of 4.1%.

a.What is the probability an individual large-cap domestic stock fund had a three-year return of at least 20% (to 4 decimals)?

What is the probability an individual large-cap domestic stock fund had a three-year return of 10% or less (to 4 decimals)?

For borrowers with good credit scores, the mean debt for revolving and installment accounts is $15,015 (BusinessWeek, March 20, 2006). Assume the standard deviation is $3,650 and that debt amounts are normally distributed.

1. What is the probability that the debt for a randomly selected borrower with good credit is more than $18,000 (to 4 decimals)?
4. What is the probability that the debt for a randomly selected borrower with good credit is less than $10,000 (to 4 decimals)?