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CHAPTER 7 REVIEW FORM A 1. Each of the following curves fails to be a normal curve. Why? (a) 1. (a) __________________________ (b) (b) __________________________ 2. According to the empirical rule, for a distribution that is symmetrical and bell-shaped, approximately _______ of the data values will lie within three standard deviations on each side of the mean. 2. ______________________________ 3. Assuming that the heights of boys in a high school basketball tournament are normally distributed, with mean 70 inches and standard deviation 2.5 inches, how many boys in a group of 40 do we expect to be taller than 75 inches? 3. _____________________________ 4.Let x be a random variable that represents the length of time it takes a student to complete Dr. Gill’s chemistry lab project. From long experience, it is known that x has a normal distribution with mean = 3.6 hours and standard deviation = 0.5 hour. Convert each of the following x intervals to standard z intervals. (a) x 4.5 4. (a) __________________________ (b) 3 x 4 (b) __________________________ (c) x 2.5 (c) __________________________ (#4 continued) Convert each of the following z intervals to raw score x intervals. (d) z 1 (d) __________________________ (e) 1 z 2 (e) __________________________ (f) z 1.5 (f) __________________________ 5. John and Joel are salesmen in different districts. In John’s district, the monthly mean sale is $17,319 with standard deviation $684. In Joel’s district, the monthly mean sale is $21,971 with standard deviation $495. Assume that sales in both districts follow a normal distribution. (a) Last month John sold $19,214 whereas Joel sold $22,718 worth of merchandise. Relative to the buying habits of customers in each district, does this mean Joel is a better salesman? Explain. 5. (a) __________________________ ____________________________ (b) Convert Joel’s sales last month to a standard z score, and do the same for John’s sales last month. Who do you think is the better salesman? (b) __________________________ 6. The length of time to complete a door assembly on an automobile factory assembly line is normally distributed with mean = 6.7 minutes and standard deviation = 2.2 minutes. For a door selected at random, what is the probability the assembly line time will be (a) 5 minutes or less? 6. (a) __________________________ (b) 10 minutes or more? (b) __________________________ (c) between 5 and 10 minutes? (c) __________________________ 7. From long experience, it is known that the time it takes to do an oil change and lubrication job on a vehicle has a normal distribution with mean = 17.8 minutes and standard deviation = 5.2 minutes. An auto service shop will give a free lube job to any customer who must wait beyond the guaranteed time to complete the work. If the shop does not want to give more than 1% of its customers a free lube job, how long should the guarantee be (round to the nearest minute). 7. _____________________________ 8. Medical treatment will cure about 87% of all people who suffer from a certain eye disorder. Suppose a large medical clinic treats 57 people with this disorder. Let r be a random variable that represents the number of people that will recover. The clinic wants a probability distribution for r. (a) Estimate P r 47 . (a) __________________________ (b) Estimate P 47 r 55 . (b) __________________________ 9. The diameters of oranges from a Florida orchard are normally distributed with mean = 3.2 inches and standard deviation = 1.1 inches. A packing supplier is designing special occasion presentation boxes of oranges and needs to know the average diameter for a random sample of 8 oranges. What is the probability that the mean diameter x for a sample of 8 oranges is (a) smaller than 3 inches? 9. (a) __________________________ (#9 continued) (b) larger than 3.5 inches? (b) __________________________ (c) between 3.1 and 3.3 inches? (c) __________________________ 10. The manufacturer of a new compact car claims the miles per gallon (mpg) for the gasoline consumption is mound shaped and symmetrical with mean = 25.9 mpg and standard deviation = 9.5 mpg. If 30 such cars are tested, what is the probability the average mpg x is (a) less than 23 mpg? 10. (a) __________________________ (b) greater than 28 mpg? (b) __________________________ (c) between 23 and 28 mpg? (c) __________________________