Question

Consider strings of length 6 which contain letters only from the set{P,Q,R,S,T} and digits from { 1,3,5,7,9}. for example TPR5Q7 is such a string. Suppose repetition allowed. 1) how many different strings are there? 2) How many of these strings have no P 3) How many of these strings have at least one P 4) How many of these strings have exactly two P's and one 7

Answer 1

Found the answer.. thanks!!!