In each of the following cases, find the mean, variance, and standard deviation of the sampling distribution of the sample proportion . (a) p = .6, n = 257 (Round variance to 6 decimal places and standard deviation to 4 decimal places. Do not round intermediate values.) (b) p = .5, n = 121 (Round variance to 6 decimal places and standard deviation to 4 decimal places. Do not round intermediate values.) (c) p = .9, n = 397 (Round variance to 6 decimal places and standard deviation to 4 decimal places. Do not round intermediate values.) (d) p = .97, n = 977 (Round variance to 6 decimal places and standard deviation to 4 decimal places. Do not round intermediate values.)