A beneficial bacterial species can double in size every hour. A batch of such bacteria will reach 1 million after 10 hours. When they reach 250,000, how many hours will it take?
一种有益的菌种每小时可增长1倍，现有一批这样的细菌，10小时后达到100万个，当它们达到25万个时，经历了多少小时？
<gadget id="calculator">10 - 2</gadget>
<output>8</output>

<result>8</result>