so according to the question, the situation is as follows:
Let the total number of the notepads equals x, so each gets x/20 in beginning and the 8 of give x/3 each to the rest 12. Corresponding the 12 receive 10 each.
So the mathematical equation of the following is:
8((2/3)(x/20))+12((x/20)+10)=x
solving for x, you get x=900;
Thus each person recieved 45 in the beginning