If the salary of a person in the base year is Rs 4,000 per annum and the current year salary is Rs 6,000, by how much should his salary rise to maintain the same standard of living if the CPI is 400?

Base CPI = Rs 100

Current CPI = Rs 400

Base Year Salary = Rs 4,000

Current Year Salary = Rs 6,000

Thus, his salary should be Rs 16,000. Therefore, in the current year his salary should increase by Rs 10,000 (i.e. Rs 16,000 – Rs 6,000) so as to maintain the same level of living in the current year as that of the base year.