If A and B are two events such that P(A) = 0.7, P(B) = 0.4 and P(A cap overlineB) = 0.5, where overlineB denotes the complement of B, then P(B | (A cup overlineB)) is equal to:

Solution & Explanation

### Related Formula P(X|Y) = fracP(X cap Y)P(Y) P(A cap overlineB) = P(A) - P(A cap B) ### Core Logic Utilize set probability laws to derive component values like the intersection P(A cap B) and basic union forms to simplify conditional constraints. ### Step 1: Evaluate Component Intersections Given P(A cap overlineB) = 0.5 and P(A) = 0.7: P(A cap overlineB) = P(A) - P(A cap B) implies 0.5 = 0.7 - P(A cap B) P(A cap B) = 0.2 ### Step 2: Calculate Set Union Compute the total area of the conditional domain set: P(A cup overlineB) = P(A) + P(overlineB) - P(A cap overlineB) P(A cup overlineB) = 0.7 + (1 - 0.4) - 0.5 = 0.7 + 0.6 - 0.5 = 0.8 ### Step 3: Resolve Final Conditional Probability Using distribution laws on intersection fields: P(B cap (A cup overlineB)) = P((B cap A) cup (B cap overlineB)) = P(A cap B) + 0 = 0.2 P(B | (A cup overlineB)) = fracP(A cap B)P(A cup overlineB) = frac0.20.8 = frac14 ### Pattern Recognition In conditional sets containing expressions like X cap (Y cup overlineX), the disjoint nature of X cap overlineX means it collapses quickly to standard overlap intersections X cap Y. ### 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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