Paper 1, Section I, F
Part IA, 2020
A robot factory begins with a single generation-0 robot. Each generation- robot independently builds some number of generation- robots before breaking down. The number of generation- robots built by a generation- robot is or 3 with probabilities and respectively. Find the expectation of the total number of generation- robots produced by the factory. What is the probability that the factory continues producing robots forever?
[Standard results about branching processes may be used without proof as long as they are carefully stated.]