2.II.9 F2 . \mathrm{II} . 9 \mathrm{~F} \quad

Probability | Part IA, 2001

I play tennis with my parents; the chances for me to win a game against Mum(M)\operatorname{Mum}(M) are pp and against Dad (D)q(D) q, where 0<q<p<10<q<p<1. We agreed to have three games, and their order can be DMDD M D (where I play against Dad, then Mum then again Dad) or MDMM D M. The results of games are independent.

Calculate under each of the two orders the probabilities of the following events:

a) that I win at least one game,

b) that I win at least two games,

c) that I win at least two games in succession (i.e., games 1 and 2 or 2 and 3 , or 1 , 2 and 3)),

d) that I win exactly two games in succession (i.e., games 1 and 2 or 2 and 3 , but not 1,2 and 3 ),

e) that I win exactly two games (i.e., 1 and 2 or 2 and 3 or 1 and 3 , but not 1,2 and 3)).

In each case a)- e) determine which order of games maximizes the probability of the event. In case e) assume in addition that p+q>3pqp+q>3 p q.

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