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?

Let the business value change from A to B.
Then, 4% of A = 5% of B
⇒ 4A/100 = 5B/100
⇒ B = 4A/5
∴ change in business = (A - 4A/5) = A/5
Percentage slump in business = {(A/5)/A} x 100 % = 20%