Bag B_1 contains 6 white and 4 blue balls, Bag B_2 contains 4 white and 6 blue balls, and Bag B_3 contains 5 white and 5 blue balls. One of the bags is selected at random and a ball is drawn from it. If the ball is white, then the probability, that the ball is drawn from Bag B_2, is:

Solution & Explanation

### Related Formula Bayes' Theorem formula: P(E_2|A) = fracP(E_2) cdot P(A|E_2)P(E_1) cdot P(A|E_1) + P(E_2) cdot P(A|E_2) + P(E_3) cdot P(A|E_3) ### Core Logic Let the events be defined as: E_1: Bag B_1 is selected E_2: Bag B_2 is selected E_3: Bag B_3 is selected A: The drawn ball is white Since a bag is selected at random: P(E_1) = P(E_2) = P(E_3) = frac13 Conditional probabilities of drawing a white ball from each bag: P(A|E_1) = frac610, quad P(A|E_2) = frac410, quad P(A|E_3) = frac510 ### Step 1: Substitute and Calculate Substituting the values into Bayes' theorem: P(E_2|A) = fracfrac13 times frac410frac13 times frac610 + frac13 times frac410 + frac13 times frac510 P(E_2|A) = frac46 + 4 + 5 = frac415 ### Pattern Recognition When bags have equal selection probability, the required conditional probability is simply the number of favorable white balls divided by the total number of white balls across all bags: 4 / (6 + 4 + 5) = 4/15. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Mathematics: Probability

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More Probability Previous-Year Questions — Page 6

Q19 jee_main_2024_31_jan_morning Variance of Random Variable
Three rotten apples are accidently mixed with fifteen good apples. Assuming the random variable X to be the number of rotten apples in a draw of two apples, the variance of X is
  • A. frac37153
  • B. frac57153
  • C. frac47153
  • D. frac40153

Solution

### Core Logic Total apples = 18 (3 rotten, 15 good). Random variable X = \0, 1, 2\ representing the number of rotten apples. ### Step 1: Probability Distribution P(X = 0) = frac^15C_2^18C_2 = frac105153 P(X = 1) = frac^3C_1 times ^15C_1^18C_2 = frac45153 P(X = 2) = frac^3C_2^18C_2 = frac3153 ### Step 2: Expectation E(X) = 0 times frac105153 + 1 times frac45153 + 2 times frac3153 = frac51153 = frac13 ### Step 3: Variance E(X^2) = 0 times frac105153 + 1 times frac45153 + 4 times frac3153 = frac57153 Var(X) = E(X^2) - (E(X))^2 = frac57153 - left(frac13right)^2 = frac57153 - frac17153 = frac40153 ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Maths: Probability

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