A small worm grows from a larva to an adult, doubles in size every day, grows to 10 cm in 10 days, how many days does it take to grow to 2.5 cm.
一条小虫，又幼虫长到成虫，每天长大1倍，10天长到10厘米，长到2.5厘米需要多少天．
<result>8</result>