the quesion is wrong. it should be -   The monthly salary of a person is increased by 10% in one month, but is decreased by 10% in the next month. What's the percentage change in his salary?   Solution: Let the initial salary be 100 tk. Increase by 10% will imply = 100 + 100x10/100 = (100 + 10) = 110 tk. Decrease by 10% will mean = 90% of 110 = 99 Hence the effective change is a decrease by = (100 - 99)% = 1%. (ans)