Let a random variable X take values 0, 1, 2, 3 with P(X = 0) = P(X = 1) = p, P(X = 2) = P(X = 3) and E(X^2) = 2E(X). Then the value of 8p - 1 is:

Solution & Explanation

### Related Formula The sum of all probabilities in a probability distribution is strictly equal to 1: sum P(X_i) = 1 ### Core Logic Let P(X=2) = P(X=3) = q. From the total probability rule: P(X=0) + P(X=1) + P(X=2) + P(X=3) = 1 p + p + q + q = 1 implies 2p + 2q = 1 implies p + q = frac12 quad dots text(i) ### Step 1: Computing Expectations Compute E(X): E(X) = 0cdot p + 1cdot p + 2cdot q + 3cdot q = p + 5q Compute E(X^2): E(X^2) = 0^2cdot p + 1^2cdot p + 2^2cdot q + 3^2cdot q = p + 13q ### Step 2: Solve the Linear System Given E(X^2) = 2E(X): p + 13q = 2(p + 5q) p + 13q = 2p + 10q implies p = 3q Substitute p = 3q into equation (i): 3q + q = frac12 implies 4q = frac12 implies q = frac18 Then, p = 3left(frac18right) = frac38. ### Step 3: Calculate 8p - 1 Now we evaluate the required expression: 8p - 1 = 8left(frac38right) - 1 = 3 - 1 = 2 ### Pattern Recognition Always combine basic distribution axioms (sum of probabilities = 1) with structural definition equations (E(X) = sum x P(x)) to systematically eliminate unknown parameters. ### 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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