The number of pages that have been read is 30 pages less than the number of pages that have not been read (4/5). If 10 pages are being read, then the number of pages that have been read is the number of pages that have not been read (3/4). How many pages does this book have?
一本已读过的页数比没读过的页数的(4/5)少30页，如果在读10页，那么读过的页数就是没读过页数的(3/4)，问这本书有多少页？
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">(3/4) * 10</gadget>
<output>15/2 = around 7.5</output>

<gadget id="calculator">30 - 10 - (15/2)</gadget>
<output>25/2 = around 12.5</output>

<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">(4/5) - (3/4)</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(25/2) / (1/20)</gadget>
<output>250</output>

<gadget id="calculator">250 * (4/5)</gadget>
<output>200</output>

<gadget id="calculator">200 - 30</gadget>
<output>170</output>

<gadget id="calculator">170 + 250</gadget>
<output>420</output>

<result>420</result>