A book is divided into two volumes. (2/7) of the pages of the first volume is equal to 25% of the pages of the second volume. It is known that the second volume has 480 pages. How many pages are there in the first volume?
一部书分上下两册，上册页数的(2/7)等于下册页数的25%，已知下册有480页，上册有多少页？
<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">(1/4) / (2/7)</gadget>
<output>7/8 = around 0.875</output>

<gadget id="calculator">480 * (7/8)</gadget>
<output>420</output>

<result>420</result>