It takes 9 seconds to count 100 exercise books. At this speed, how many seconds will it take to count 10,000 exercise books?
数100本练习本要用9秒，照这样的速度，数10000本练习册大约要用多少秒．
<gadget id="calculator">9 / 100</gadget>
<output>9/100 = around 0.09</output>

<gadget id="calculator">(9/100) * 10_000</gadget>
<output>900</output>

<result>900</result>