Question

The mean and variance of a binomial distribution are 6 and 4. The parameter n is

• A. 18
• B. 12
• C. 10
• D. 9

Answer 1

Answer: (A)

18

Answer 2

Given $n p = 6 , n p q = 4$

∴ $\frac { n p q } { n p } = \frac { 4 } { 6 } \Rightarrow q = \frac { 2 } { 3 }$ and $p = \frac { 1 } { 3 }$

$\bullet \bullet$ $n p = 6 \Rightarrow n \times \frac { 1 } { 3 } = 6$ $\Rightarrow n = 18$ .