CA Foundation · Quantitative Aptitude · Theoretical Distributions
A fair coin is tossed 4 times. What is the probability of getting exactly 2 heads?
The probability is 3/8. Exactly two heads in four tosses can occur in 4C2 = 6 ways, and each sequence has probability (1/2)^4 = 1/16. Multiplying gives 6/16, which equals 3/8.
- A1/4
- B3/8Correct
- C1/2
- D5/16
Explanation
P(X=2) = 4C2 × (1/2)^2 × (1/2)^2 = 6/16 = 3/8. The value 1/4 ignores the number of arrangements, taking only (1/2)^2. The value 1/2 is wrongly treating 2 heads of 4 as a 50% chance.
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