There are 10 tons of coal, 10% of which is used for the first time, and (1/10) tons are used for the second time, how many tons of coal are left.
有10吨煤，第一次用去10%，第二次用去(1/10)吨，还剩下多少吨煤．
<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">10 * (9/10)</gadget>
<output>9</output>

<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">9 - (1/10)</gadget>
<output>89/10 = around 8.9</output>

<result>89/10 = around 8.9</result>