9 different possible tiles to choose, but there are duplicates of two types of tiles. Out of 9 tiles, two of them are S. Therefore, the probability you choose an S is 2/9 (however much percent that is).
You'd reverse the math for letters other than P:
Out of 9 tiles, two of them are P. 9 minus 2 is seven. Seven out of 9 characters are not the letter P. Therefore, the probability you choose any letter other than P is 7/9 (however much percent <em>that </em>is).
