A small worm grows from a larva to an adult, doubling in size every day, and grows to 10 cm in 10 days. How many days does it take to grow to 2.5 cm.
一条小虫，由幼虫长大到成虫，每天长1倍，10天长到10厘米．长到2.5厘米需多少天．
<gadget id="calculator">2.5 * 4</gadget>
<output>10</output>

<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">10 - 2</gadget>
<output>8</output>

<result>8</result>