ISI2017-DCG-28

Question

A basket contains some white and blue marbles. Two marbles are drawn randomly from the basket without replacement. The probability of selecting first a white and then a blue marble is $0.2$. The probability of selecting a white marble in the first draw is $0.5$. What is the probability of selecting a blue marble in the second draw, given that the first marble drawn was white?

• A. $0.1$
• B. $0.4$
• C. $0.5$
• D. $0.2$

Comments

b?

Answer 1

Let E be the event of selecting White marble and F be the event of selecting blue marble P(E∩F)=0.2 P(E)=0.5 we have to find P(F/E) According to conditional probability P(F/E)=P(E∩F)/P(E)=0.2/0.5=0.4 so option b

Answer 2

I think the answer should be B) 0.4

Explanation : Probability given that selecting a white marble and then blue marble P(AnB) = 0.2 and probability given that first marble is white P(B) = 0.5

We are need to find conditional probability given already that first marble is white so : P(AnB)/P(B) = 0.4 is the answer