CA Foundation · Quantitative Aptitude · Theoretical Distributions
A coin is biased so that the probability of heads is 0.4. If it is tossed 50 times, what is the standard deviation of the number of heads?
The standard deviation is √12, about 3.46. The variance of the binomial is npq, which is 50 × 0.4 × 0.6 = 12, and the standard deviation is its square root.
- A20
- B√20
- C√12Correct
- D12
Explanation
Variance = npq = 50 × 0.4 × 0.6 = 12. Standard deviation = √12 ≈ 3.46. Choosing 20 gives the mean np, which is not the standard deviation.
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