ProbabilityHard

Question

In a purse there are 10 coins, all 5 paise except one which is a rupee. In another purse there are 10 coins all 5 paise. 9 coins are taken out from the former purse & put into the latter & then 9 coins are taken out from the latter & put into the former. Then the chance that the rupee is still in the first purse is:

Options

A.9/19
B.10/19
C.4/9
D.none

Solution

10 coins    9       5 paisa        10 coins    5 paisa
                 1        1 Rs.
p = p (1 Rs. transfered + Back transfered) + p (1 Rs. not transfered)

      
method 2 when 1 Rs coin is in second purse and did not came back in first purse this prob. =
⇒   Required probability = 1 -

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