There is a difference of 20 tons between A and B piles of coal, how many tons is the difference between the two piles of coal after 10% of each is shipped out?
甲、乙两堆煤相差20吨，各运出10%后，两堆煤相差多少吨．
<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">1 - (1/10)</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">100 * (9/10)</gadget>
<output>90</output>

<gadget id="calculator">80 * (9/10)</gadget>
<output>72</output>

<gadget id="calculator">90 - 72</gadget>
<output>18</output>

<result>18</result>