Suppose, according to a 1990 demographic report, the average u. s. household spends $90 per day. suppose you recently took a random sample of 30 households in huntsville and the results revealed a mean of $84.50. suppose the standard deviation is known to be $14.50. using a 0.05 level of significance, a. can it be concluded that the average amount spent per day by u. s. households has decreased? ( provide 2 approached both the "t-test" and "p-value" approach.) b. create the 95 % confidence interval for the population mean using the information above?