The story books in the school accounted for (3/5) of the total number of books in the school. After buying 400 story books, the story books accounted for (2/3) of the total. How many books did the school have?
学校的故事书占全校图书总数的(3/5)，又买进400本故事书后，这时故事书占总数的(2/3)，问学校原来共有多少本图书？
<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 - (3/5)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(3/5) / (2/5)</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">1 / (3/2)</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">1 - (2/3)</gadget>
<output>1/3 = around 0.333333</output>

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

<gadget id="calculator">3 / 2</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">2 - (3/2)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">400 / (1/2) / (2/5)</gadget>
<output>2_000</output>

<result>2_000</result>