Abakery sold an average (arithmetic mean) of 820 cookies per day in an operating period. on "good" days, the bakery sold an average of 980 cookies per day, and on "fair" days, the bakery sold an average of 640 cookies per day. if every day in the operating period was either "good" or "fair," what was the ratio of the number of "good" days to the number of "fair" days for the bakery’s operating period?