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 answer.
A) 8 %	B) 1 %	C) 20 %	D) 80 %	E) none

Rationale: answer let the business value change from a to b . then , 4 % of a = 5 % of b ⇒ 4 a / 100 = 5 b / 100 ⇒ b = 4 a / 5 ∴ change in business = ( a - 4 a / 5 ) = a / 5 percentage slump in business = { ( a / 5 ) / a } x 100 % = 20 % correct option : c
Answer: C