Question

If cov$(x,y)$ is $1.85$, $\sum xy=321$, $\overline{x}=5.5,\overline{y}=5.5$ the value of $n$(number of observation ) is

• A. $11$
• B. $12$
• C. $10$
• D. $45$

Answer 1

Answer: (C)

$10$

$cove(x,y)=\frac{\sum xy-n\overline{x}\overline{y}}{n}$

$\Rightarrow$ $1.85=\frac{321-n\left(5.5\right)\left(5.5\right)}{n}$

$\Rightarrow$ $1.85n=321-30.25n$

$\Rightarrow$ $1.85n+30.25n=321$

$\Rightarrow$ $32.1n=321$

$\Rightarrow$ $n=\frac{321}{32.1}$

$\therefore$ $n=10$