If you bind a book with 500 characters per page, you can arrange 180 pages. If you change it to 600 characters per page, how many pages can you save? (Solve with ratio)
装订一本书，如果每页排500个字，可以排180页，如果改为每页排600个字，可以少排多少页？(用比例解)
<gadget id="calculator">500 * 180</gadget>
<output>90_000</output>

<gadget id="calculator">90_000 / 600</gadget>
<output>150</output>

<gadget id="calculator">180 - 150</gadget>
<output>30</output>

<result>30</result>