Answer:
The answer is 120 pages are filled with hockey cards
Step-by-step explanation:
So, first find out what the remaining percentage is, in this case it is 20%
Then use a calculator (or if your that smart and can do it in your head which i applaud) fine 20% of 600, which is 120. So that's how many pages there are left. Just to double check find out what 80% of 600 is which is 480. Then you should add those together to see if you get the total amount of cards. Which, 120+480 does equal 600.
I hope this helps <3