Solution

ID: past-exam-of-the-year-1-of-the-computer-science-course-of-the-university-of-oxford/2015/digital-systems-linear-algebra-introduction-to-formal-proof-resit/5/c/solution

Condition on the intermediate parent's height and use the Markov property. The three mutually exclusive paths through Tall, Medium and Short contribute
Equivalently, this is entry of the matrix power . Hence

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