 Solution

ID: past-exam-of-the-mathematics-course-of-the-year-1-of-the-natural-sciences-course-of-the-university-of-cambridge/2015/paper-1/16/a/iv/solution

P (B_{1} \cup B_{2}) = \frac{4}{7} + \frac{4}{7} - \frac{2}{7} = \frac{6}{7} .

As a check, its complement is two white draws, with probability

(3/7) (2/6) = 1/7

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