A shopping mall buys 80 yuan per pair of leather shoes and sells them at a price increase of 50%. When half of the total amount is left, the cost is still 4,000 yuan. When a fraction of the total amount is sold, can the cost be recovered?
某商场购进每双80元的皮鞋，加价50%出售，当还剩总数的一半时，还欠成本4000元，当卖出总数的几分之几时，才能正好收回成本？
<gadget id="calculator">400 / 3</gadget>
<output>400/3 = around 133.333333</output>

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

<gadget id="calculator">80 * (1/2)</gadget>
<output>40</output>

<gadget id="calculator">50 / 100</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">80 * (1/2) * (1/2)</gadget>
<output>20</output>

<gadget id="calculator">80 - 40 - 20</gadget>
<output>20</output>

<gadget id="calculator">4_000 / 20</gadget>
<output>200</output>

<gadget id="calculator">(400/3) / 200</gadget>
<output>2/3 = around 0.666667</output>

<result>2/3 = around 0.666667</result>