A pile of 400 kilograms of coal, 50% of it is used for the first time, and the remaining 50% is used for the second time, how many kilograms of this pile of coal are left
一堆煤400千克，第一次用去50%，第二次用去剩下的50%，这堆煤还剩下多少千克
<gadget id="calculator">50 / 100</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 - (1/2)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) * (1/2)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/2) - (1/4)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">400 * (1/4)</gadget>
<output>100</output>

<result>100</result>