Income tax is raised from 4 paise to 5 paise in a rupee but the revenue is increased by 10% only. Find the decrease percent in the amount taxed.

Let the original taxed amount be Rs. x and new taxed amount be Rs. y
Let the original revenue be Rs. 100
Then, 4% of x = 100 or
x = $$\left( {\frac{{100 \times 100}}{{4}}} \right)$$
x = Rs. 2500
New revenue = 110% of Rs. 100 = Rs. 110
Then, 5% of y = 110 or
y = $$\left( {\frac{{110 \times 100}}{{5}}} \right)$$
y = Rs. 2200
Decrease in taxed amount :
= Rs. (2500 - 2200)
= Rs. 300
∴ Decrease % :
$$=$$$${\text{ }}\left( {\frac{{300}}{{2500}} \times 100} \right)$$
$$= 12$$ %