If the original salary was Rs.100 and the new salary is Rs.90,
then the decrease in salary is Rs.10.
The increase on Rs.90 is Rs.10, which is a 10/90 = 11.11% increase.
The increase on Rs.100 is ((10/90)*100)% = (100/9)% = 11.11% increase.
To express the increase as a percentage, you can use the formula:
percent increase = (new value - old value)/old value * 100%