A reads a book, reads 20% of the total pages of the book on the first day, reads 30 pages less than the first day on the second day, and reads exactly 35% of the total pages of the book in two days. How many pages are there in the book?
甲读一本书，第一天读了全书总页数的20%，第二天比第一天少读了30页，两天正好读了全书总页的35%．全书共多少页？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">35 / 100</gadget>
<output>7/20 = around 0.35</output>

<gadget id="calculator">(7/20) - (1/5)</gadget>
<output>3/20 = around 0.15</output>

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

<gadget id="calculator">30 / (1/20)</gadget>
<output>600</output>

<result>600</result>