The average weight of 30 persons is increased by 2 kg. when one of them whose weight is 40 kg. is replaced by a new person. What is the weight of the new person?

Correct option is B

​$$\textbf{Given:} \\\text{Average weight increases by } 2 \text{ kg for } 30 \text{ persons} \\\text{Weight of person replaced} = 40 \text{ kg} \\\textbf{Formula:} \\\text{Total increase in weight} = \text{Increase in average} \times \text{Number of persons} \\= 2 \times 30 = 60 \text{ kg} \\\textbf{Therefore:} \\\text{New person's weight} = \text{Old weight} + \text{Total increase} \\= 40 + 60 = {100 \text{ kg}}$$

Correct answer is (b) 100 kg.