I agree with Joost Elshoff , but i think you have a good reason to do
so
i may use Stash
make 10 coins
put each 1 coin in a label
each label is restriced by view one of the pdf otherwise hidden ( for best results use another restriction to re hide the label after show it and get the coin , i made this before )
so when student collect 8 coins , give him access to what you need
sorry for quick and incomplete reply , but i know you are not a beginner and will get the idea easily .
so
i may use Stash
make 10 coins
put each 1 coin in a label
each label is restriced by view one of the pdf otherwise hidden ( for best results use another restriction to re hide the label after show it and get the coin , i made this before )
so when student collect 8 coins , give him access to what you need
sorry for quick and incomplete reply , but i know you are not a beginner and will get the idea easily .