The state test scores for 12 randomly selected high school seniors are shown on the right. Complete parts (a) through (c) below. 1420 1226 982 725 840 Assume the population is normally distributed. 692 730 748 546 624 1448 947 (a) Find the sample mean. x= 910.7 (Round to one decimal place as needed.) (b) Find the sample standard deviation. s = 303.8 (Round to one decimal place as needed.) (c) Construct a 90% confidence interval for the population mean u. A 90% confidence interval for the population mean is ) (Round to one decimal place as needed.)