Since 1950, global paper consumption has increased by more than 6 times, and the paper industry has used one-fifth of the world's harvested wood. Let's save paper. The printing room of the school purchased a new pack of white paper, planning to use 50 sheets per day, which can be used for 10 days. Due to paying attention to saving paper, only 25 sheets are actually used every day. How many days are actually used? (answer with ratio)
自1950年以来，全球纸张消耗量增加了6倍多，造纸业用去了世界采伐木材的五分之一，让我们节约用纸吧．学校打印室新购一包白纸，计划每天用50张，可以用10天．由于注意了节约用纸，实际每天只用了25张，实际用多少天？(用比例解答)
<gadget id="calculator">50 * 10</gadget>
<output>500</output>

<gadget id="calculator">500 / 25</gadget>
<output>20</output>

<result>20</result>