Question

Mean of $9$ observations was founded to be $35$. Later on, it was detected that an observation $81$ was misread as $18$, then the correct mean of the observations is ____________.

• A. $40$
• B. $41$
• C. $42$
• D. $43$

Answer 1

The correct option is C $42$

Mean of $9$ observations $=35$

Sum of $9$ observations $=35\times 9=315$

Since $81$ was misread as $18$

New sum $=315-18+81=378$

The correct mean $=\frac{378}{9}=42$