After 20% of 250 kilograms of coal is used up, the remaining 20% is used up, how many kilograms are used in two times
250千克煤用去20%后，又用去余下的20%，两次一共用去多少千克
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">250 * (1/5)</gadget>
<output>50</output>

<gadget id="calculator">250 - 50</gadget>
<output>200</output>

<gadget id="calculator">200 * (1/5)</gadget>
<output>40</output>

<gadget id="calculator">50 + 40</gadget>
<output>90</output>

<result>90</result>