One hundred draws are made at random with replacement from box A, and 250 are made at random with replacement from box B.
a) 50 of the draws from box A are positive, compared to 131 from box B: 50.0% versus 52.4%. Is this difference real, or due to chance?
b) The draws from box A average 1.4 and their SD is 15.3; the draws from box B average 6.3 and their SD is 16.1. Is the difference between the averages statistically significant?