Question

The mean of $20$ observations is $15$. On checking, it was found that two observations were wrongly copied as $3$ and $6$. If wrong observations are replaced by correct values $8$ and $4$, then the correct mean is

• A. $15$
• B. $15.15$
• C. $15.35$
• D. $16$

Answer 1

Answer: (B)

$15.15$

Mean $=15$ for $20$ observations

$\therefore$ Sum of total observations for mean $=15\times 20=300$

For correcting the total, we have to subtract $3,6$ from total and add $8,4$

Correct total $=300-3-6+8+4=303$

Correct mean $=\frac{303}{20}=15.15$

Hence, B is correct.