The science and technology books in the school library account for 60% of the total number of books in the school, and 400 science and technology books are purchased. At this time, the science and technology books account for 2/3 of the total. How many books are there in total?
学校图书馆中科技书占全校图书总数的60%，又买进400本科技书，这时科技书占总数的(2/3)，原来共有多少本图书．
<gadget id="calculator">60 / 100</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>