The tax on a commodity is diminished by 20% but its consumption is increased by 20%. Find the decrease percent in the revenue derived from it? Pick one:
A) 20%
B) 18%
C) 4%
D) 12%
E) 14%
100 * 100= 
<gadget id="calculator">100 * 100</gadget>
<output>10_000</output>
10000   80 * 120= 
<gadget id="calculator">80 * 120</gadget>
<output>9_600</output>
9600   10000------- 400   100 ------- ?= 4%   ANSWER:4%
<result>C</result>
The tax on a commodity is diminished by 20% but its consumption is increased by 20%. Find the decrease percent in the revenue derived from it?