Solution

ID: past-exam-of-the-year-1-of-the-computer-science-course-of-the-university-of-oxford/2019/discrete-mathematics-continuous-mathematics-and-probability/2/a/solution

Use the inclusion-exclusion principle on the multiples of in . The pairwise least common multiples are , and the triple least common multiple is . Therefore the count is
The endpoint is excluded, which is why the numerators are rather than .

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