5.5 help teacher is a mofe

A drug company tested a new drug on 250 pigs with swine flu. Historically, 20% of pigs contracting swine flu die from the disease. Of the 250 pigs treated, 215 recovered. Estimate the probability that this result is by chance.

Please somebody help. the class average for our classes last unit test was 14%. Our teacher is such a mean sob he says its our fault...this is a question on the make-up test and i still dont get it. Also, share your horrible teacher stories, itll be hilarious stuff.