Given: The average monthly salary of a person is 50000. Formula used: Sum of observations = average × numbers of observations Calculation: Yearly total salary paid =50000×12=600000 Overtime of 2 months when he earns 6000 extra per month = 2 × 6000 = 12000 ∴ Correct yearly salary = 600000 + 12000 = 612000 ∴ Correct monthly income of person = 612000 / 12 = 51000 Short trick: Increase in yearly salary because of overtime of 2 × 6000 = 12000 ∴ Increase in monthly salary =