Air quality in Boston is generally very good: during the ten-year period 2004–2013, there were only 4 days in which the air was unhealthy for the general public, according to the EPA.
How many days between 2004 and 2013 was the air unhealthy?
4 days
Air quality in Boston is generally very good: during the ten-year period 2004–2013, there were only 4 days in which the air was unhealthy for the general public, according to the EPA.
Air quality in Boston is generally very good: during the ten-year period two thousand four-twenty thirteen, there were only four days in which the air was unhealthy for the general public, according to the EPA.
How many days between two thousand four and twenty thirteen was the air unhealthy?