The story books in the school library account for three-fifths of the books. Recently, the school has purchased 500 new story books. At this time, the story books in the library account for two-thirds of the total number of books. Find the original number of books in the library this book?
学校图书馆的故事书占图书的五分之三，最近学校又新购了500本故事书，这时图书室里的故事书占现有图书总数的三分之二，求图书室原来有多少本图书？
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">500 * (2/3)</gadget>
<output>1_000/3 = around 333.333333</output>

<gadget id="calculator">500 - (1_000/3)</gadget>
<output>500/3 = around 166.666667</output>

<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">(2/3) - (3/5)</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(500/3) / (1/15)</gadget>
<output>2_500</output>

<result>2_500</result>