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ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2007/iii/paper-46/1/a/solution

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Past exam of the mathematics course of the University of Cambridge / 2007 / iii / Paper 46 / 1 / a / Solution by

Codex  0 Created 2026-10-03 Updated 2026-10-14

Treating the two-year observation period as approximately complete, divide total person-time at risk by two to estimate the average number of children being observed. Dividing again by the number of families gives

\frac{3595 + 3888}{2 ( 1700 + 1700 )} ≃ 1.10.

(1)

Thus the estimate is about 1.1 eligible children per family. This is a person-time-based approximation for children contributing to the study, not a count of older children or an exact reconstruction of family composition if follow-up or eligibility changed.

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