Test. mz Question 10 This Test: 135 pts possible Submit Test According to a report from a business intelligence company, smartphone owners are using an average of 19 apps per month. Assume that number of apps used per month by smartphone owners is normally distributed and that the standard deviation is 4. Complete parts (a) through (d) below. a. If you select a random sample of 36 smartphone owners, what is the probability that the sample mean is between 18.5 and 19.5? (Round to three decimal places as needed.) b. If you select a random sample of 36 smartphone owners, what is the probability that the sample mean is between 18 and 19? (Round to three decimal places as needed.) c. If you select a random sample of 144 smartphone owners, what is the probability that the sample mean is between 18.5 and 19.5? (Round to three decimal places as needed.) d. Explain the difference in the results of (a) and (c). The sample size in (c) is greater than the sample size in (a), so the standard error of the mean (or the standard deviation of the sampling distribution) in (c) is than in (a). As the standard error values become more concentrated around the mean. Therefore, the probability that the sample mean will fall close to the population mean will always when the sample size increases