The question is: pennies come in rolls of 50. Out of the 200 rolls a bank is storing, 12 have all Canadian pennies: the remaining 188 rolls contain at least one American penny. In the 200 rolls, about how many American pennies are there? What is the median number of American pennies per roll?
I can't fathom how derive any sort of probability from so little information. I get the median would be at the 50th percentile, but with this information, how is finding a median and mean possible?
I'd start with the binomial distribution:
$$P(C = 200) = \binom{200}{200} p^{200}(1 - p)^{0}\\ = \frac{12}{200} = \frac{6}{100}$$.
Knowing that, you can estimate the probability that any single coin is Canadian.