The ratio of the number of books on the upper shelf to the number of books on the middle shelf is 5:3, and the ratio of the number of books on the middle shelf to the number of books on the lower shelf is also 5:3. There are 1000 books on the upper shelf. How many books are there on the lower shelf?
书架上层书本数与中层书本数的比是5：3，中层书与下层书本数的比也是5：3，上层书有1000本，求下层有书多少本？
<gadget id="calculator">1_000 / 5</gadget>
<output>200</output>

<gadget id="calculator">200 * 3</gadget>
<output>600</output>

<gadget id="calculator">600 / 5</gadget>
<output>120</output>

<gadget id="calculator">120 * 3</gadget>
<output>360</output>

<result>360</result>