CA Foundation · Quantitative Aptitude · Theoretical Distributions
A Poisson random variable X has a variance of 4. What is the standard deviation of X?
The standard deviation is 2. In a Poisson distribution the mean and variance are both equal to the parameter m, so the variance of 4 gives a standard deviation equal to its square root, which is 2.
- A16
- B4
- C2Correct
- D8
Explanation
For a Poisson distribution, mean equals variance, so m = 4. The standard deviation is the square root of the variance, which is √4 = 2. The value 4 is the variance, not the standard deviation, so it is wrong.
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