Question

The variance of $3,6,9,\dots .,30$ is

• A. $72.45$
• B. $74.25$
• C. $54.36$
• D. $48.37$

Answer 1

The correct option is B $74.25$

${\sigma }^2=\frac{3^2+6^2+...+{30}^2}{10}-{\left(\frac{3+6+....+30}{10}\right)}^2$
$=9(\frac{385}{10}-\frac{3025}{100})=9\left(\frac{3850-3025}{100}\right)$
$=74.25$