SOLUTION: Roll a die once. Then roll it as many times as the outcome from the first roll. Getting the special number "3" on any roll means a win. What is the expected number of wins from thi

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Question 1178261: Roll a die once. Then roll it as many times as the outcome from the first roll. Getting the special number "3" on any roll means a win. What is the expected number of wins from this experiment?
Answer by robertb(5830) About Me  (Show Source):
You can put this solution on YOUR website!
Let X = r.v. equal to the value of the die on the 1st throw.
Then for X = 1, 2, 3, 4, 5, 6, it can be shown combinatorially that P%28X+=+x%29+=+1%2F6%5E2+%2B+5%2F6%5E3++...+5%5E%28x-1%29%2F6%5E%28x%2B1%29+=+%281%2F6%29%2A%281-%285%2F6%29%5Ex%29.
The probability of a '3' turning up on any throw is 1/6. Hence the expectation for the number of wins in this game is

to 2 d.p.