How do i solve these?

2) A bag contains red and blue marbles totaling between 50 to 100 in number. If two marbles are drawn at random, the chances of them both being red are 25%. One third of the marbles are picked from the bag and thrown away. If one marble is now drawn at random from the bag, what is the probability of it being blue? (Answer in %)

---- My workings:

For the 2nd one:

I assumed the set of marbles to be 6, since the answer is supposed to be in % and the 50 to 100 range seems absurd. So, 25% of

6 will be 2 red marbles. Rest are 4 blue marbles. 1/3rd of the total set is removed randomly which makes it obvious that two blue marbles were the ones removed. So, my answer sums up to 50% of blue balls. The answer is correct but am not sure of my logic.