CA Foundation · Quantitative Aptitude · Theoretical Distributions
A fair coin is tossed 3 times and X denotes the number of heads. What is the probability distribution value P(X >= 2)?
P(X >= 2) is 1/2. With three fair tosses, exactly two heads has probability 3/8 and three heads has probability 1/8. Adding them gives 4/8 equal to 1/2. Counting only exactly two heads would wrongly give 3/8.
- A3/8
- B1/2Correct
- C1/4
- D7/8
Explanation
X is binomial with n = 3, p = 1/2. P(X=2) = 3C2/8 = 3/8 and P(X=3) = 1/8. Sum = 4/8 = 1/2. The value 3/8 counts only exactly two heads and omits the case of three heads.
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