Question

If the frequencies of first four numbers out of $1,2,4,6,8$ and $2,3,3,2$ respectively, then find the frequency of $8$ if their $A.M.$ is $5$, is

• A. $4$
• B. $5$
• C. $6$
• D. none of these

Answer 1

The correct option is C $6$

Here mean $A=5$.
Let the frequency of $8$ be $x$. Then by the formula

$A=\frac{\sum xf}{\sum f}=\frac{1.2+2.3+4.3+6.2+8.x}{2+3+3+2+x}$

$\therefore 5=\frac{32+8x}{10+x}$

$\therefore 18=3x$

$\therefore x=6$