Question

The mean of $18,24,15,2x+1$ and $12$ is $21$, then the value of $x$ is:

• A. $17$
• B. $17.5$
• C. $18$
• D. $7.5$

Answer 1

The correct option is B $17.5$

The given observations are : $18,24,15,2x+1,12$.

We know, Mean is given by,

$\text{Mean}=\frac{\text{Sum of the elements}}{\text{Total number of elements}}$.

Here, number of observations $=5$.

$⟹$ Mean $=\frac{18+24+15+2x+1+12}{5}$

$⟹$ $\frac{18+24+15+2x+1+12}{5}$ = $21$

$⟹70+2x=105$

$⟹2x=105-70=35$

$⟹$ $x=\frac{35}{2}=17.5$.

Therefore, option $B$ is correct.