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#33879

counting

probability

hard

90 sec

A bag contains only red and blue marbles. The number of red marbles is $r$ , and the number of blue marbles is $b$ . If the probability of selecting a red marble from the bag is $\frac{1}{3}$ , and there are 12 more blue marbles than red marbles, how many red marbles are in the bag?

• Up to 5 characters (6 if negative). Only numbers, decimal (.), fraction (/), negative (-).
• Fractions must be in lowest terms.
• Mixed numbers must be converted to improper fractions.