It is known that under ordinary conditions, 15% of people will not contract a certain disease. Consider the situation where test groups of 500 were selected and the percentages of those who did not contract the disease were recorded.

According the Central Limit Theorem, percentages of groups of 500 who don't contract the disease are approximately normally distributed. Find the mean and standard deviation of this normal distribution. Round the standard deviation to one decimal place.

mean = 250%, standard deviation = 2.6%

mean = 15%, standard deviation = 1.6%

mean = 85%, standard deviation = 1.6%

mean = 15%, standard deviation = 2.6%