Question

If the variance of the random variable $X$ is $5$, then the variance of the random variable $-3X$ is

• A. $15$
• B. $45$
• C. $-45$
• D. $60$

Answer 1

Answer: (B)

$45$

We know that
${\sigma }_{a+bx}^2={b^2\sigma }^2$
Here $a=0,b=-3$
$\Rightarrow {\sigma }^2$ for $-3X=9\ast 5=45$