A book has 500 pages, number the pages 1, 2, 3, 4, 5... Ask how many times the number "1" appears in the page number.
一本书有500页，编上页码1、2、3、4、5…问数字"1"在页码中出现了多少次．
<gadget id="calculator">500 / 100</gadget>
<output>5</output>

<gadget id="calculator">5 * 10</gadget>
<output>50</output>

<gadget id="calculator">50 + 50 + 100</gadget>
<output>200</output>

<result>200</result>