Use num_rows (and arithmetic) to find the proportion of movies in the dataset that were released 1900-1999, and the proportion of movies in the dataset that were released in the year 2000 or later.
Assign proportion_in_20th_century to the proportion of movies in the dataset that were released 1900-1999, and proportion_in_21st_century to the proportion of movies in the dataset that were released in the year 2000 or later.
Hint: The proportion of movies released in the 1900's is the number of movies released in the 1900s, divided by the total number of movies.

num_movies_in_dataset = num_in_20th_century = num_in_21st_century = proportion_in_20th_century = mdb.where('Year', are.below(2000)).num_rows / num_movies_in_dataset
proportion_in_21st_century = imdb.where('Year', are.above_or_equal_to(2000)).num_rows / num_movies_in_dataset

print("Proportion in 20th century:", proportion_in_20th_century)
print("Proportion in 21st century:", proportion_in_21st_century)