There are several table tennis balls in the box, 25% of which are first-class products, (2/5) are second-class products, and the remaining 91 are third-class products. How many table tennis balls are there in the box?
箱子里有兵乓球若干个，其中25%是一级品，(2/5)是二级品，其余的91个是三级品，箱子里一共有兵乓球多少个？
<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (1/4) - (2/5)</gadget>
<output>7/20 = around 0.35</output>

<gadget id="calculator">91 / (7/20)</gadget>
<output>260</output>

<result>260</result>