The weight of a person was entered incorrectly as 83 kg instead of 63 kg. As a result, the average weight of a group of people increased by 500 gm. What is the total number of people in the group?

Answer: Option C

Let, number of peoples in group = x
Average = n
⇒ nx - 63 + 83 = n(x + 500 gm)
⇒ nx + 20 = nx + $$\frac{\text{n}}{2}$$ kg
⇒ n = 20 × 2
⇒ n = 40

OR
$$\begin{array}{rl}& \text{Average}=\frac{\text{Sum}}{\text{Number}}\\ & 500\text{gm}=\frac{20}{n}\\ & \frac{1}{2}=\frac{20}{n}\\ & n=40\end{array}$$