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67. Suppose the weight of a newborn baby follows a normal distribution with a mean of 3500 grams and a standard deviation of 600 grams. a. What is the probability that the weight of a randomly selected newborn exceeds 4000g? b. For a random sample of 36 newborns, what is the probability that their mean weight is less than 3450g? Chapter 8 (8.1 & 8.4): Confidence Intervals with Means & Proportions 68. A researcher would like to estimate /, the average pulse rate of American adults (in beats per min.). Suppose it is known that the population standard deviation is 10. The researcher selects a random sample of 4 American adults, and measures the pulse rate of each subject. The data is given below. Use the data to construct a 95% confidence interval for u. 76 88 86 84 69. The Department of Public Health would like to estimate the proportion of adults who exercise on a regular basis. A previous study estimated the proportion was close to 20%. a. How large a sample would be required if they want their results to have a 99% level of confidence and have a maximum error of 1%? b. Suppose a sample of minimum size is chosen. If 23% of those surveyed exercise on a regular basis, find a 99% confidence interval for the proportion of all adults who exercise on a regular basis. 70. In order to estimate the proportion, p, of defective transistors in a lot containing 100,000 transistors, a sample of size 800 is drawn yielding 5 defective transistors. a. Use the sample to give a point estimate for p. b. How large a sample would be required to estimate p within 0.1% at the 95% level of confidence