 Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2025/ib/paper-1/19h/c/solution

Codex  0 Created 2026-09-24 Updated 2026-09-25

After the forced first step

A \to B

, let

h_{i} = P_{i} (T_{A} < T_{F})

. Symmetry gives

h_{C} = h_{D} = x

, while

h_{B} = (1 + 2 x) /3, x = (h_{B} + h_{E}) /2, h_{E} = 2 x /3.

Solving gives

h_{B} = 2/3

. Thus the requested probability is

2/3

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