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4.Average
hard
If the mean of $5$ observation $x, x+2, x+4, x+6$ and $x+8$ is $11,$ then the mean of the last three observations is
A
$11$
B
$13$
C
$15$
D
$17$
Solution
Mean of 5 observations given.
$\frac{x+x+2+x+4+x+6+x+8}{5}=11$
$x+4=11$
$x=11-4=7$
Mean of last $3$ observations $=\frac{x+4+x+6+x+8}{3}=x+6=7+6=13$
Standard 13
Quantitative Aptitude