Asurvey of 50 retail stores revealed that the average price of a microwave was $375, with a sample standard deviation of $20 (i. e. the population standard deviation was not known). assuming the population is normally distributed, what is the 95% confidence interval to estimate the true cost of the microwave? a) $323.40 to $426.60b) $328.40 to $421.60c) $350.80 to $395.80d) $369.31 to $380.69