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There are 5 blue marbles, 4 red marbles, and 3 yellow marbles in a box. If Jim randomly selects a marble from the box, what is the probability of selecting a red or yellow marble?

A \( \frac{\mathrm{7} }{\mathrm{12} } \)

A probability is the likelihood of a successful event occurring divided by the total number of events possible. In this case, a successful event is selecting either a red or a yellow marble and the total number of events possible is the total number of marbles. Combine the number of red and yellow marbles: 4 + 3 = 7, and divide this by the total number of marbles: 5 + 4 + 3 = 12. The probability is \( \frac{\mathrm{7} }{\mathrm{12} } \)