Question

The mean of $20$ observations was found to be $16.5$. It was later discovered that one observation was wrongly copied as $12$ instead of $21$. Find the correct mean

• A. $16.95$
• B. $17.85$
• C. $16.59$
• D. $17.58$

Answer 1

The correct option is A $16.95$

The mean of $20$ observation is $16.5$

$\Rightarrow$ Sum of $20$ observation $=20\times 16.5=330$

It is given that one observation wrongly copied as $12$ instead of $21$

$\therefore$ Correct sum of $20$ observations $=330-12+21=339$

$\therefore$ Required mean $=\frac{339}{20}=16.95$