The average marks of four subjects is 120. If 33 was misread as 13 during the calculation, what will be the correct average?

Answer: Option C

$$\begin{array}{rl}& \text{Correct average}\\ & =120+\left(\frac{33-13}{4}\right)\\ & =120+5\\ & =125\end{array}$$
Solve while reading method:
Average given is 120.
Difference of 33 and 13 is 20.
That means 20 must be added to total.
Then average of is and so must be added to average, i.e.
Correct average = 120 + 5 = 125