There are 50 bottles of pure water in the box. After 20% of the bottles are sold, they are filled with 20% of the remaining pure water in the box. How many bottles of pure water are there in the box?
箱内有50瓶纯净水，卖出20%后，又装入箱内所剩纯净水的20%，这时箱中有多少瓶纯净水．
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 + (1/5)</gadget>
<output>6/5 = around 1.2</output>

<gadget id="calculator">50 * (4/5) * (6/5)</gadget>
<output>48</output>

<result>48</result>