Q2 of 19 Page 302

A box contains 5 green, 8 yellow and 7 brown balls. One ball is taken out from a box at random. What is the probability that the ball taken out is (i) yellow ? (ii) brown? (ii) neither green nor brown ? (iv) not brown?

Number of green balls in the box = 5

Number of yellow balls in the box = 8


Number of brown balls in the box = 7


Total number of balls including green, yellow and brown in the box = 5 + 8 + 7 = 20


Now, let the event that a green ball is taken from the box be G.


the event that a yellow ball is taken from the box be Y.


the event that a green ball is taken from the box be B.


Number of favourable outcomes of event G = 5


Number of favourable outcomes of event Y = 8


Number of favourable outcomes of event B = 7


Total number of favourable outcomes = 5 + 8 + 7


= 20


(i) Probability of a yellow ball to be taken from the box = Probability of event Y occurring = P(Y)


P(Y) =


(ii) Probability of a brown ball to be taken from the box = Probability of event B occurring = P(B)


P(B) =


(iii) Probability of the taken ball is nether green nor brown = 1 – Probability of ball taken is either green or brown = 1- P(G or B)


P(G or B)’ = 1-P(G or B)


=


=


(iv) Probability of the ball taken is not brown = 1-Probability of the ball taken is brown = 1-P(B)


P(B’) = 1- P(B)


=


=


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