Given P(X = 2) = 0.3, P(X = 3) = 0.4, P(X = 4) = 0.3. What is the variance of X? A) 0.3. B) 0.6. C) 3.0. D) 0.5. Your answer: A was incorrect. The correct answer was B) 0.6. The variance is the sum of the squared deviations from the expected value weighted by the probability of each outcome. The expected value is E(X) = 0.3 × 2 + 0.4 × 3 + 0.3 × 4 = 3. The variance is 0.3 × (2 − 3)(sq) + 0.4 × (3 − 3)(sq) + 0.3 × (4 − 3)(sq) = 0.6. This question tested from Session 2, Reading 8, LOS k Based on the question, why would we not want to divide the sum of the weighted squared deviations by n (or n-1)
You have probabilities given… which has taken into account already the # of items and their distribution. 0.3+0.4+0.3 = 1.0 (Total probability) This is an example of calculation when provided a Probability Distribution function. CP
This is one of those questions in which you can actually use your calculator. Take the “divide by n” variance of 2,2,2, 3,3,3,3,4,4,4 using whatever are the suitable keys.
makes sense Thx.