CA Foundation · Quantitative Aptitude · Theoretical Distributions
A fair coin is tossed 4 times. What is the probability of getting exactly 3 heads?
The probability is 1/4. With n = 4 and p = 1/2, the chance of exactly 3 heads is 4C3 times (1/2) to the power 4, which equals 4/16 or 1/4. Ignoring the combination factor would wrongly give 1/16.
- A1/16
- B1/2
- C3/8
- D1/4Correct
Explanation
P(X=3) = 4C3 × (1/2)^3 × (1/2)^1 = 4 × 1/16 = 1/4. The option 1/16 omits the coefficient 4C3, so it is wrong.
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