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Tom keeps all of his favorite marbles in a special leather bag. Right now, five red marbles, four blue marbles, and three yellow marbles are in the bag. 

  1. If he randomly chooses one marble to give to a friend, what is the probability that it is blue?

    How many blue marbles are in the bag? How many marbles are there total?

  2. Tom does not really want to give away blue marbles and would like to change the probability that he chooses a blue marble to . How many marbles that are not blue could he add to the bag so that the probability of choosing a blue marble becomes ?

    If four blue marbles and eight non-blue marbles make a probability of , how many non-blue marbles do you need to combine with blue marbles to achieve a probability of ?: