gmat question

This is GMT question the answer is D. but I am little bit confused if someone know please solve this question I will be grateful to you .

Q - If the value of a piece of property decreases by 10 % while the tax rate on the property increases by 10 %, what is the effect on the taxes?

a) Taxes increases by 10 %

b) Taxes increases by 1 %

c) No change

d) Taxes decreases by 1 %

e) Taxes decreases by 10 %

Let say Price is P,
Price increase rate is I = 10%
Tax is T = 10%

then formula to calculate the tax should be

= P - ( P x I ) ] x T

If you caclulate the tax using this formula and then the simple tax calculating formula i.e.

= P x T

then there should be difference of 1% from actual price.

I hope it makes some sense.

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I think this belongs in the C&A section. Don't you think! :)