JEE Main 2019 (Online) 11th January Evening ShiftQuestion 1
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, then $\left(\frac{\text{mean of }X}{\text{standard deviation of }X}\right)$ is equal to :
Probability
Solution
Binomial $n=16$, $p=\frac34$: mean $=12$, variance $=16\cdot\frac34\cdot\frac14=3$, sd $=\sqrt3$. Ratio $=\frac{12}{\sqrt3}=4\sqrt3$.