The sixth grade office bought a pack of white paper, and planned to use 25 sheets per day, which can be used for 20 days. Because of saving paper, the actual use is only 10 sheets per day. How many days can it be used? (Solve with ratio)
六年级办公室买进一包白纸，计划每天用25张，可以用20天，由于注意了节约用纸，实际每天只用10张，实际能用多少天？(用比例解)
<gadget id="calculator">25 * 20</gadget>
<output>500</output>

<gadget id="calculator">500 / 10</gadget>
<output>50</output>

<result>50</result>