The income of a broker remains unchanged though the rate of commission is increased from 4% to 5%. The percentage of slump in business is :
Choose the correct choice from the following choices
A) 8 %  B) 1 %  C) 20 %  D) 80 %  E) none

Rationale: "explanation : let the business value changes from x to y . then , 4 % of x = 5 % of y or 4 / 100 × x = 5 / 100 × y or y = 4 / 5 x change in business = ( x − 4 / 5 x ) = 1 / 5 x percentage slump in business = ( 1 / 5 x × 1 / x × 100 ) % correct option : c"
Answer: C