Q. 113.9( 7 Votes )

A bag contains 18

Answer :

(i) Total numbers of elementary events are 18


Let E be the event of getting not red ball


Let A be the event of getting a red ball


The number of favourable events are x


P (red ball) =P (A) = x/18


P (not red ball) = P (E) = 1 – x/18


(ii) Two ball are added to the existing 18 balls


Total numbers of elementary events are: 18 + 2 = 20


Let E be the event of getting a red ball


P (red ball) = P (E) = (x + 2) /20


According to the given condition


(X + 2) /20 = 9/8 x (x/18)


(x + 2) /20 = x/16


4x + 8 = 5x


X = 8 being the initial numbers of red ball.


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