 Solution

ID: past-exam-of-the-mathematics-course-of-the-year-1-of-the-natural-sciences-course-of-the-university-of-cambridge/2023/paper-2/14/b/iii/solution

Choose the unordered pair of letters in the second bin; the first bin is then determined. The binomial coefficient gives

(2 6) = \frac{6 !}{4 ! 2 !} = 15 .

The first and second bins are distinguished, so their roles are not interchangeable.

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