Question

The mean of $20$ observations is $12.5$. By error, one observation was noted as $-15$ instead of $15$. Then the correct mean is __________.

• A. $11.75$
• B. $11$
• C. $14$
• D. $13$

Answer 1

Answer: (C)

$14$

Mean of $20$ observations $=12.5$

Sum of $20$ observations $=12.5\times 20=250$

Since $15$ was misread as $-15$

New sum $=250-(-15)+15=280$

The correct mean $=\frac{280}{20}=14$