Answer:
a. 11/25
b. 11/25
Step-by-step explanation:
We proceed as follows;
From the question, we have the following information;
Three urns A, B and C contains ( 3 black balls 7 white balls), (7 black balls and 13 white balls) and (12 black balls and 8 white balls) respectively.
Now,
Since events of choosing urn A, B and C are denoted by Ai , i=1, 2, 3
Then , P(A1 + P(A2) +P(A3) =1 ....(1)
And P(A1):P(A2):P(A3) = 1: 2: 2 (given) ....(2)
Let P(A1) = x, then using equation (2)
P(A2) = 2x and P(A3) = 2x
(from the ratio given in the question)
Substituting these values in equation (1), we get
x+ 2x + 2x =1
Or 5x =1
Or x =1/5
So, P(A1) =x =1/5 , ....(3)
P(A2) = 2x= 2/5 and ....(4)
P(A3) = 2x= 2/5 ...(5)
Also urns A, B and C has total balls = 10, 20 , 20 respectively.
Now, if we choose one urn and then pick up 2 balls randomly then;
(a) Probability that the first ball is black
=P(A1)×P(Back ball from urn A) +P(A2)×P(Black ball from urn B) + P(A3)×P(Black ball from urn C)
= (1/5)×(3/10) + (2/5)×(7/20) + (2/5)×(12/20)
= (3/50) + (7/50) + (12/50)
=22/50
=11/25
(b) The Probability that the first ball is black given that the second ball is white is same as the probability that first ball is black (11/25). This is because the event of picking of first ball is independent of the event of picking of second ball.
Although the event picking of the second ball is dependent on the event of picking the first ball.
Hence, probability that the first ball is black given that the second ball is white is 11/25
