It is known that in the absence of treatment, 55% of the patients with a certain illness will improve. The Central Limit Theorem tells us that the percentages of patients in groups of 400 that improve in the absence of treatment are approximately normally distributed.
(a) Find the mean and standard deviation of the normal distribution given by the Central Limit Theorem. Round the standard deviation to one decimal place.
mean
%
standard deviation
%

(b) In what percentage of such groups (of 400) would 215 or fewer improve? Round your answer to one decimal place.
%