300
What is the difference between these two sentences:
By the year 2020, people will have watched TV for 80 years.
By the year 2020, people will have been watching TV for 80 years.
By the year 2020, people will have watched TV for 80 years.
... emphasis is on the "completion" of 80 years (but it could still continue beyond 2020).
By the year 2020, people will have been watching TV for 80 years.
... emphasis is on the "duration" of watching (and will likely continue beyond 2020).