Question

If the mean of five observations $x,x+2,x+4,x+6,x+8$ is $11$ then the mean of first three observations is

• A. $9$
• B. $11$
• C. $13$
• D. None

Answer 1

The correct option is A $9$

Since, Mean = $\frac{x+(x+2)+(x+4)+(x+6)+(x+8)}{5}$
$\Rightarrow 11=\frac{5x+20}{5}$
$\Rightarrow 55=5x+20$
$\Rightarrow 35=5x$
$\Rightarrow x=7$
$\therefore$ First three observations $x,x+2,x+4$ becomes 7, 9, 11
Mean of the first three observations is:
$\frac{7+9+11}{3}=\frac{27}{3}=9$
$\therefore$ Option A is correct.