[13. A psychologist claims that the mean age at which children start walking is 19 months. EkHEi wanted to check ifthis claim is me. He took a random sample of 25 children and found that the mean age at which these children started walking was '1? months with a standard deviation of 3 months. it is known that the ages at which all children start walking are approximately normally distributed. Test that the mean age at which all children start walking is less than 19 months at 53-3 level of signicance. A company wanted to know if attending a course on \"how to be a successful salesperson\" can increase the average sales of its employees. The company sent six of iE salespersons to attend this course. The fol lowing table gives the 1week sales of these salespersons before and after they attended this course. \"1o 15 1o 11 11 11 _11 11 1s 11 11 15 Using the 5315. significance level, can you conclude that the mean weekly sales for all salespersons increase as a resuft of attending this course? Assume that the population of paired differences has a normal dist n' bution. A EDGE survey of low- and middle-income households conducted by Demos; a liberal public group, showed that consumers aged 65 years and older had an average credit card debt of $1y535 and consumers in the 5-0- to 64year age group had an average credit card debt of $9642 at the time of the survey {LISA TDDA'I': July 23, mos}. Suppose that these averages were based on random samples of 12130: and 14013 people for the two groups; respectively. Further assume that the population standard deviations for the two groups were $300 and $2-, respectively. Let p1 and p2 be the respective population means for the two groups, people aged 55 years and older and people in the 53 to 64year age group. [a] Construct 96913 confidence interval for 111 p2 and interpret the results. {[11 Mention the margin of error