In an auditorium, 1/3of the 900 seats are empty and 2/3of the total seats (900)are filled after 1 hour. Then, the auditorium is

Answer 1

You may either want the fraction full, the fraction empty, the number of seats full, or the number of seats empty... you have not actually asked a question.
But...
If we figure out how many seats are EMPTY at the end of the hour you can figure the rest out.
At the start 1/3(900) are empty... so 300 empty, and 600 at the beginning are full.
After 1 hour 2/3 of the seats are now full (of the 300 still empty)
so...
2/3(300) = 200
So at the end of 1 hour there are 200 of the 900 still empty : )