According to a 2007 survey of CEOsof major corporations conducted by financial solutions,%48 "would choose the same career if they were starting over again".In a similar survey conducted 10 years ago,60% of the CEOs said that they would choose the same career if they starting over again.800 CEOs were used in the 2007 survey and only 600 CEOs were used in the 1997 survey
a)Construct a 95% confidence interval for the difference between the two populatin proportions
b)Test at 5% significance level whether the proportion of all CEOs who would choose the same career if they were starting over again has decreased during past 10 years