Question 1133760
If his salary is reduced by x%, his new salary is (100-x)/100 of his original salary, expressed as a fraction.  
To get back the original amount, we need to multiply by 100/(100-x).
For example, if his salary is reduced by 20%, the new salary is 0.8 times the original salary. 
So we need to multiply by 1/0.8 = 1.25, or 125%.