Q. 11 In a game, a man wins a rupee for a six and loses a rupee for any other number when a fair die is thrown. The man decided to throw a die thrice but to quit as and when he gets a six. Find the expected value of the amount he wins / loses.
In a throw of die,
probability of getting six = P
probability of not getting six = q
There are three cases :
1. Gets six in the first throw, required probability is
The amount he will receive is Re. 1
2.. Does not gets six in the first throw and gets six in the second throw, then the probability
The amount he will receive is - Re.1+ Re.1=0
3. Does not gets six in first 2 throws and gets six in the third throw, then the probability
Amount he will receive is -Re.1 - Re.1+ Re.1= -1
Expected value he can win :