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Total number of students with siblings = 2 (has a brother) + 2 (has a sister) = 4
Total number of students = 2 (has a brother) + 5 (does not have a brother) + 4 (has a sister) + 19 (does not have a sister) = 30
Probability that a student chosen randomly from the class has a sibling = 4/30 = 2/15 = 0.1333
Therefore, the probability that a student chosen randomly from the class has a sibling is 0.1333 or 13.33%.