9. A furniture manufacturer has found that the time spent by workers assembling a particular table follows a normal distribution with a mean of 150 minutes and a standard deviation of 40 minutes. a. The probability is 0.9 that a randomly chosen table requires more than how many minutes to assemble? b. The probability is 0.8 that a randomly chosen table can be assembled in fewer than how many minutes? 10. A company services copier. A review of its records shows that the time taken for a service call can be represented by a normal random variable with a mean of 75 minutes and a standard deviation of 20 minutes. a. What proportion of service calls takes less than 1 hour? b. What proportion of service calls takes more than 100 minutes? 11. Scores on an achievement test are known to be normally distributed with a mean of 420 and a standard deviation of 80. a. what is the probability of a score between 400 and 480? b. What is the minimum test score needed in order to be in the top 10% of all people taking the test