An economics professor told his students that, instead of spending hundreds of dollars for a very accurate watch, they should wear 20 cheap watches and calculate the average time shown on these 20 watches. Suppose that the reported time on each cheap watch is normally distributed with a mean equal to the actual time and a standard deviation of 10 seconds and the errors in the reported times on all the cheap watches are independent of each other. What are the mean and standard deviation of the average time on these 20 watches?