Question

A bag contains $30$ white balls and $10$ red balls. $16$ balls are drawn one by one randomly from the bag with replacement. If X be the number of white balls drawn, the $\left(\frac{\text{mean} \; \text{of} \; X}{\text{standard} \; \text{deviation} \; \text{of} \; X }\right)$ is equal to :

• A. $4$
• B. $\frac{4 \sqrt{3}}{3}$
• C. $4 \sqrt{3}$
• D. $3 \sqrt{2}$

Answer 1

Answer: (C)

$4 \sqrt{3}$

Answer 2

p (probability of getting white ball) = $\frac{30}{40}$
$q = \frac{1}{4}$ and n = 16
mean =np = $16 . \frac{3}{4} = 12$
and standard diviation
$= \sqrt{npq} = \sqrt{ 16 . \frac{ 3}{4} . \frac{1}{4}} = \sqrt{3}$