Income tax is raised-from 4% to 5% but the revenue is increased by 10% only. Find the decreased percentage in the amount taxed.

Let the original taxed amount be Tk. x and
new taxed amount be Tk. y
Let the original revenue be Tk. 100
Then, 4% of Tk. x = 100
or, x = (100 × 100)/4 = Tk. 2500
New revenue = 110% of Tk. 100 = Tk. 110
Then, 5% of Tk. y = 110
or, y = (110×100)/5 = Tk. 2200
Decrease in taxed amount = Tk. (2500 - 2200) = Tk. 300
∴ Decrease % = (300/2500) ×100 = 12%