QUESTION 45 Questions 44 - 51 concern the following idea: Bob runs a phone company called Phantastic Phones. He conducts a survey on a random sample of 500 of his customers, in which he asks questions about their phone use habits, expenditure on phones, and so on. The sample mean of the value of each customer's phone when new was $486.23 with a sample standard deviation of $170.49. He had hoped to be able to estimate the mean to within $9 with 95% accuracy but realised that 500 is too few. Using these figures, how many customers should Bob have surveyed to be able to achieve this? (round your answer to next highest integer). QUESTION 46 Questions 44 - 51 concern the following idea: Bob runs a phone company called Phantastic Phones. He conducts a survey on a random sample of 500 of his customers, in which he asks questions about their phone use habits, expenditure on phones, and so on. The survey showed that the sample proportion of customers who had a pre-paid plan was 0.52. Calculate the standard error associated with this estimate (correct to 4 dp)