371 The Environmental Protection Agency reports that the mean concentration of the greenhouse gas carbon dioxide is 365 parts per million (ppm). Suppose that the population is approximately normally distributed with a standard deviation 0* of 100 ppm. 3. Find the probability that a city selected at random will have a carbon dioxide level above 400 ppm. b. A random atmospheric sample of 100 cities is obtained. Find the mean and standard error of the distribution of sample means of size 100. c. Find the probability that a random sample of size 100 will have a mean carbon dioxide level above 400 ppm