A bookshelf has three layers. It is known that the upper layer (1/5) is equal to the middle layer (1/4) and the lower layer (1/6). It is known that there are 750 books in this bookshelf. How many books are there in the middle?
一个书架有三层，已知上层的(1/5)等于中层的(1/4)等于下层的(1/6)，已知这个书架共有750本书．中层有多少本书？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/5) / (1/4)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">(1/5) / (1/6)</gadget>
<output>6/5 = around 1.2</output>

<gadget id="calculator">1 + (4/5) + (6/5)</gadget>
<output>3</output>

<gadget id="calculator">750 / 3</gadget>
<output>250</output>

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

<result>200</result>