The tax on an article decreases by 10% and its consumption

The tax on an article decreases by 10% and its consumption increases by 10%. Find the effect per cent on its revenue.

Let the original consumption be 1 unit & tax on it be ₹100.
So, revenue = ₹(100 × 1) = ₹100.
New consumption

=		110	× 1		=	11	units.
		100				10

Now, tax on 1 unit = ₹90

Tax on	11	units
	10

=		90 ×	11		= ₹ 99.
			10

∴ Decrease in revenue = 1 %