A piece of work, A and B work together for 4 hours to complete 25% of it, and then B does it alone for 8 hours. At this time, A alone needs 20 hours to complete the remaining work. A alone does this How long does the job take?
一件工作，先由甲、乙合做4时，完成了它的25%，再由乙单独做8时，这时剩下的工作甲单独做还需20时才能全部完成，甲单独做这件工作需多长时间？
<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/4) * 2</gadget>
<output>1/2 = around 0.5</output>

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

<gadget id="calculator">20 - 8</gadget>
<output>12</output>

<gadget id="calculator">(1/4) / 12</gadget>
<output>1/48 = around 0.020833</output>

<gadget id="calculator">1 / (1/48)</gadget>
<output>48</output>

<result>48</result>